IRLF 


EXCHANGE 


Dehydrothiotoluidin:    Its  Isomers, 

Homologues,  Analogues,  and 

Derivatives. 


DISSERTATION 


SUBMITTED    IN    PARTIAL    FULFILLMENT    OF    THE    RE- 
QUIREMENTS  FOR   THE    DEGREE   OF   DOCTOR   OF 
PHILOSOPHY    IN    THE    FACULTY    OF    PURE 
SCIENCE  OF  COLUMBIA  UNIVERSITY 


BY 


MARTIN  MEYER,  B.S.,  M.A. 


NEW  YORK  CITY 
1921 


Dehydrothiotoluidin:    Its  Isomers, 

Homblogues,  Analogues,  and 

Derivatives. 


DISSERTATION 


SUBMITTED    IN    PARTIAL    FULFILLMENT    OF    THE    RE- 
QUIREMENTS   FOR    THE    DEGREE    OF    DOCTOR    OF 
PHILOSOPHY    IN    THE    FACULTY    OF    PURE 
SCIENCE  OF  COLUMBIA  UNIVERSITY 


BY 

MARTIN  MEYER,  B.S.,  M.A. 

NEW  YORK  CITY 
1921 


«    .  '. 


ACKNOWLEDGMENT   AND    DEDICATION 


To  Professor  Marston  Taylor  Bfogert  to  whose  inspiration, 
suggestion,  and  constant  interest,  such  merit  as  this  work  may 
possess  is  due. 

M.  M. 


ORGANIC  RESEARCH  LABORATORIES,    .. 
HAVEMEYER  HALL,  COLUMBIA  UNIVFRSHY, 
MAY,  1921 


CONTENTS 

I.     Acknowledgment  and  Dedication 2 

II.     Introduction  and  Purpose 5 

III.  Historical  Review  of  Previous  Work 6 

IV.  Appendix  to  the  Historical  Review 20 

V.     Experiments  - 21 

Part  A — Benzothiazoles  21 

1.  Oxalaminothiophenol   21 

2.  Para   toluyl   nitrile   22 

3.  Paratoluic  acid  22 

4.  Paratoluyl   chloride  .. 22 

o.  Paratolanilide  22 

6.  2-Paratolyl-benzothiazole  (A)   22 

7.  Thiocarbanilide  23 

8.  Phenyl  Mustard  Oil  23 

9.  Thioparatolanilide  !. 23 

10.  Paratolyl  benzothiazole  (B)  24 

11.  2-Phenylamino-benzothiazole  25 

1.2.  Tri   (2-anilinobenzothiazolyl)  Carbinol  27 

13.  Di-benzothiazolyl-Fuchsone-Benzothiazolyli- 

mine  28 

14.  Sulphonation  of  the  Dye 28 

15.  Nitrotolyl  benzothiazole  28 

16.  Aminotolyl  benzothiazole  20 

17.  Azo  Dyes  from  Amino  paratolyl  benzothia- 

zole    29 

18.  Para  (2  Benzothiazolyl)  benzoic  acid  30 

19.  Primiline  azo  benzoylene  urea.....* 31 

Part  B— Dehydrothioluidin  32 

1.  The  Casella  Method  33 

2.  The  Kalle  Method  ...  34 


4^3563 


3.  Attempt  to  develop  a  New  Synthesis  of  De- 

hydrothiotoluidin    

4.  Paranitrobenzal    paratoluidin    

5.  Fusion  of  Para  nitrobenzalparatoluidin  with 

sulphur  >i4 

6.  Fusion  of  Para  nitrotoluene  with  sulphur oS 

7.  Apparatus  for  the  Vacuum  Distillation  of  De- 

hydrothiotoluidin  38 

8.  Preparation  of  Pure  Dehydrothiotoluidin 41 

9.  Benzal  dehydrothiotoluidin  41 

10.  Dehydrothiotoluidin  in  the  Atophan  Reaction  42 

11.  6   (6  methyl  benzothiazolyl)   quinolin  42 

VI.     Discussion  and   Conclusions  44 

VII.     Summary  45 

VIII.     Bibliography  46 

IX.     Biographical  Note  48 


Dehydrothiotoluidin:    Its  Isomers, 

Homologues,  Analogues,  and 

Derivatives. 


Introduction  and  Purpose 

The  chemistry  of  the  organic  sulphur  compounds  is  one  of 
the  widest  and  most  interesting  divisions  of  the  broad  arid  attrac- 
tive extent  of  the  science,  and  in  variety  of  properties,  multiplicity 
of  applications,  and  novelty  of  the  reactions  involved,  is  at  least 
equal  to,  and  certainly  is  excelled  by  no  other.  No  matter  what 
we  choose  as  the  criterion  of  our  judgment  we  can  meet  afl  of 
the  requirements  without  pa'ssing  the  boundaries  of  this  field,  be 
it  medicinals,  perfumes,  dyes,  explosives,  or  plastics,  there  is 
hardly  a  reaction  that  does  not  find  its  analogue,  and  in  addi- 
tion there  are  many  here  that  can  not  be  duplicated  elsewhere. 

In  the  chemistry  of  the  dyestufTs,  however,  the  sulphur  com- 
pounds are  pre-eminent.  Of  all  the  glorious  colors  which  the 
chemist  has  contributed  to  mankind  in  his  efforts  to  duplicate 
the  iridescent  beauty  of  the  rainbow,  the  most  beautiful  and  per- 
manent are  found  in  this  group,  the  sulphides,  the  thioindigos,  the 
thiazines,  the  thiazoles,  and  many  others,  the  mere  enumeration 
of  which  with  their  classes  and  sub-classes  would  fill  a  volume. 

Among  the  most  interesting  of  all  from  both  academic  and 
commercial  standpoints  are  the  five-membered  nitrogen  and  sul- 
phur heterocycles,  more  particularly  the  six-five  bicyclic  ones,  or 
benzothiazoles.  Of  these  the  simplest  is  benzothiazole,  or  methe- 
nyl  base  as  it  is  termed  by  Hofmann,  to  which  the  indicated 
structure  is  assigned.  It  may  be  observed  that  two 


arrangements  of  the  atoms  in  the  smaller  ring  are  possible.  The 
nomenclature  of  the  typical  five-membered  heterocycle  is  given 
by  Richter  as  follows  : 

—  CHB 


and  in  this  system  all  of  the  compounds   mentioned  herein  are 
substituted  beta-thiazoles,  the  principal  substitution  being  the  in- 


corporation  of  the  alpha-beta  carbon  atoms  into  a  second  benzol 
nucleus.  The  compound  shown  above  is  then  benzo-beta-thiazole, 
and  it  is  further  suggested  that  for  the  sake  of  simplicity  in 
nomenclature  the  positions  in  this  be  numbered  as  shown,  which 
is  also  more  in  uniformity  with  the  system  appled  to  the  thiazines 
and  other  heterocyclic  compounds.  This  will  be  followed  through- 
out this  paper. 

The  homologues  and  derivatives  of  the  compound  just  given 
offer  a  peculiarly  attractive  field  for  research,  because  of  the 
variety  of  their  properties  and  their  commercial  importance.  To 
substantiate  this  statement  without,  at  this  point,  going  into  too 
much  detail,  a  few  examples  may  be  cited.  By  the  fusion  of 
benzanilide  with  sulphur,  A.  W.  Hofmann  prepared  what  he 
called  benzenylortho-aminothiophenol,  which  in  the  system  just 
recommended,  is  2-phenyl-benzothiazole.  The  compound,  wholly 
unlike  any  other  known  substance  of  its  type,  has  a  pleasant, 
highly  aromatic  odor,  somewhat  suggestive  of  tea-roses  or  gera- 
niums, which  led  its  discoverer  to  term  it  also  "Rosenkorper." 
Some  of  the  derivatives  of  this  series  are  dyes.  A.  H.  Green,  on 
fusing  paratoluidin  with  sulphur,  found  primulin  and  dehydrothio- 
toluidin,  which  are  well  known  because  of  their  practical  value, 
since  the  annual  production  of  direct  cotton  dyes  exceeds  all  others, 
being  closely  rivalled  only  by  acid  wool  colors,  and  all  the  dyes 
of  this  group  are  direct  cotton  colors. 

The  last-named  two  substances  are  formed  simultaneously  in 
the  same  reaction,  and  it  is  an  odd  coincidence  that  while  imme- 
diately after  the  original  work,  the  former  was  the  important 
product,  today  the  latter  is  the  more  valuable.  Nevertheless,  in 
recent  years  comparatively  little  work  has  been  done,  or  at  any 
event,  has  been  published,  with  them,  and  up  to  the  present  no 
entirely  satisfactory  method  has  been  developed  for  preparing 
dehydrothiotoluidin  in  a  state  of  purity,  and  the  discovery  of  one 
would  probably  make  it  an  even  more  important  intermediate 
than  it  is.  Further  study  of  the  reaction  by  which  it  is  formed 
is  therefore  highly  desirable. 

With  this  brief  introduction,  the  objects  of  this  dissertation 
may  be  stated  as  follows: 

1.  To   make   some    further   contributions  to   the   chemistry   of 
the  benzothiazole  group. 

2.  To  derive  a  relation  between  the  thiazole  structure  and  tinc- 
torial value. 

3.  To   determine   the   relation   between  the   thiazole    structure 
and  odor. 

4.  To   prepare    pure    dehydrothiotoluidin    (6    methyl    2    para- 
aminophenyl  benzothiazole)  and  to  separate  it  from  the  primulin 
simultaneously  formed. 

Historical  Review  of  Previous  Work 

Although  the  volume  of  research  which  has  been  accomplished 
in  this  field  is  quite  large,  and  the  compounds  important,  most 


textbooks  omit  it  entirely  or  dismiss  it  with  a  few  lines,  and 
even  the  original  papers  do  not  give  much  information  about 
other  work.  No  really  acceptable  summary  of  all  of  the  work 
has  ever  been  published,  and,  as  it  would  be  very  useful  to  new 
investigations  in  the  group,  it  is  this  which  has  led  to  the  rather 
complete  form  in  which  the  history  is  presented.  Furthermore, 
the  second  and  third  objects  of  this  investigation  make  a  knowl- 
edge of  what  compounds  have  been  prepared,  and  of  their  proper- 
ties essential,  and  these  are  given  at  the  end. 

The  credit  for  the  discovery  of,  and  original  work  upon  the 
compounds  of  this  group  belongs  to  August  Wilhelm  von  Hof- 
mann  (born  April  8,  1818,  died  May  5,  1892),  one  of  Liebig's 
illustrious  pupils,  and  without  whose  work  organic  chemistry,  as 
we  know  it  today,  would  indeed  be  much  the  poorer.  As  his 
biographers,  Jacob  Volhard  and  Emil  Fischer,  whose  pre-eminence 
in  chemistry  needs  no  further  eulogy,  say  i1 

"Out  of  the  great  number  of  chemists  who,  come  forth  from 
Liebig's  school  in  the  second  half  of  the  last  century,  have  made 
themselves  useful  as  teachers  and  investigators  in  the  broadening 
and  advancing  of  our  knowledge,  August  Wilhelm  von  Hofmann 
towers  above  all  others  in  the  number  and  importance  of  his 
discoveries,  in  the  success  of  his  teaching,  in  the  fruitfulness  of 
his  influence  on  the  chemical  industry,  and  in  the  range  of  his 
directing  influence  as  an  author."  Not  the  least  among  these 
were  his  researches  upon  the  benzothiazoles. 

In  1874,  Sell  and  Zierold2  succeeded  in  preparing  isocyan- 
phenyl-chloride  from  phenyl  mustard  oil  by  the  direct  action  of 
chlorine.  A  few  years  later  Hofmann3  conceived  the  idea  of 
making  the  same  substance  from  the  mustard  oil  using  PC15,  ex- 
pecting that  the  reaction  would  take  place  in  this  manner: 
C7H5NS  +  PC15  =  C7H5NC12  +  PC13S 

Upon  actually  performing  the  experiment  he  found  that  while 
some  of  the  substance  was  indeed  changed  in  this  way,  distilla- 
tion of  the  reaction  products  yielded  a  portion  boiling  at  248°  C. 
that  contained  a  chlorinated  mustard  oil  of  a  totally  different 
type.  The  new  substance  was  an  oil  of  aromatic  odor,  B.P. 
248°  C.,  soluble  in  alcohol,  from  which  it  was  precipitated  by 
water,  and  upon  a  complete  elementary  analysis  as  a  basis  he 
assigned  the  empirical  formula  C7H4NSC1  to  it.  It  did  not 
resemble  in  the  least  the  compound  for  which  he  had  been  look- 
ing, and  he  proceeded  to  investigate  its  reactions.  By  acid  hydro- 
lysis he  obtained  C7H4NS(OH)  as  a  white  solid  (M.P.  136°, 
Jacobson  later  139°),  which  exhibited  phenolic  properties,  so  he 
assumed  the  presence  of  an  hydroxyl  group.  Diinner4  had  pre- 
viously prepared  hydroxy-phenyl  mustard  oil  which  did  not  re- 
semble this  compound.  The  action  of  ammonia  on  the  compound 
yielded  the  amine  as  an  oil  of  aromatic  odor,  while  aniline  gave 
the  anilide,  a  white,  odorless  solid  (M.P.  159°).  Although  at 


this  time  he  really  did  no  work  upon  the  structure  of  these  sub- 
stances, they  were  the  first  of  the  benzothiazoles,  for  as  he 
showed  later,  they  are  all  2-substituted  derivatives. 

During  the  same  year5  Hofmann  became  interested  in  a  dif- 
ferent type  of  sulphur  compound.  Merz  and  Weith6  had,  by 
the  action  of  sulphur  on  aniline,  obtained  a  thioaniline  which 
later  proved  to  be  identical  with  that  prepared  by  KrafFt7  who 
demonstrated  that  it  was  a  phenyl  sulphide.  It  occurred  to  Hof- 
mann that  if,  instead  of  employing  aniline,  he  used  benzanilide, 
or  as  he  called  it,  phenyl-benzamide,  in  place  of  NH2C6H4 — S— 
C6H4NH2,  he  should  obtain  a  benzoylated  thioaniline.  On  ac- 
tually performing  the  experiment  he  found  a  reaction  quite  dif- 
ferent from  his  expectations,  and  prepared  in  this  way  a  sub- 
stance which  crystallized  from  alcohol  in  colorless  needles  (M.P. 
115°  C.)  and  had  a  pleasant,  fragrant  odor,  resembling  tea-roses 
or  geraniums.  Analysis  indicated  the  empirical  formula  C13H9NS, 
and  he  showed  the  reaction  by  which  it  was  formed  to  be : 
C13HnNO  +  S  =  C18H9NS  -f  H20 

Hobrecker8  earlier  had  synthesized  a  compound  to   which  he 
assigned  the  formula 

/MH\ 

CH,C.H,<     ,C-CH, 


by  reducing  nitro-acetorthotoluidid,  and  Ladenburg,9  and  later 
Wund,10  had  prepared  similar  bases  by  the  condensation  of  dia- 
mines  with  acids,  and  finally,  studying  the  condensation  of  ortho- 
aminophenols  with  acids,  Ladenburg11  had  made  a  substance 
which  he  wrote 

< 

CtH. 

The  analogy  to  his  own  case  was  immediately  apparent,  and 
Hofmann  assigned  the  formula  _ 


to  the  "Rosenkorper."  To  establish  this  fact  more  definitely, 
he  then  proceeded  to  show  that,  as  would  be  expected  from  its 
structure,  it  yields,  on  hydrolysis,  orthoamino-thiophenol  and  ben- 
zoic  acid,  and  that  it  could  be  prepared  from  these  two  by  the 

/NHCOQH. 

formation  of  an  intermediate       C4H4v 

XSH 

This  was  the  first  compound  of  the  group  whose  structure  could 
in  any  sense  be  said  to  have  been  proved.  He  now  went  back 
to  his  original  chlorphenyl  mustard  oil  and  repeated  his  work, 

8 


adding  some  more,  and  preparing  a  number  of   new  compounds 
listed  at  the  end  of  the  section. 

Then  realizing  that  his  previous  article  contained  no  proof  of 
the  structure  of  the  chlor  mustard  oil,  he  proceeded  to  investigate 
its  reactions  still  further.  By  reduction  with  tin  in  concentrated 
hydrochloric  acid,  he  obtained  C7H5NS,  a  liquid,  heavier  than 
water  and  insoluble  in  it,  soluble  in  ethyl  alcohol  and  carbon 
disulphide,  having  a  burning  taste,  and  a  characteristic  odor  re- 
sembling somewhat  that  of  the  pyridines  and  the  plant  bases.  It 
is  isomeric  with  the  mustard  oils  and  thiocyanates  and  forms  an 
addition  product  with  methyl  iodide  which  is  soluble  in  water 
from  which  it  crystallizes  in  colorless  needles,  M.P.  210°.  The 
new  base  reacted  with  benzoyl  chloride — 

C7HSNS  +  C7H5OC1  =  C13H9NS  +  CO  +  HC1 
This  compound  proved  to  be  identical  with  that  which  he  had 
previously  obtained  by  the  fusion  of  benzanilide  with  sulphur, 
and  established  beyond  reasonable  doubt,  the  structure  of  the  new 
substances,  which  he  then  named  on  this  basis.  By  this  method 
he  contributed  further  new  compounds  listed  at  the  end. 

Up  to  this  time  the  only  general  method  by  which  the  benzo- 
thioazoles  could  be  prepared,  which  was  recognized  as  such,  was 
that  by  which  the  just  mentioned  ones  were  prepared,  that  is, 
the  condensation  of  ortho-aminothiophenols  and  acids,  acid  an- 
hydrides, chlorides,  and  amides,  but  also  in  188012  he  conceived 
the  idea  that  the  reaction  by  which  "Rosenkorper"  had  been 
synthesized  might  be  applied  with  appropriate  changes  to  the  syn- 
thesis of  homologues.  Immediately  he  proceeded  to  investigate 
the  behaviour  of  anilides  on  fusion  with  sulphur,  obtaining  from 
formanilide  a  small  amount  of  methenyl  base  or  benzothiazole, 
from  acetanilide  slight  quantities  of  ethenyl  base,  or  2-methyl 
benzothiazole,  but  much  larger  yields  of  a  new  substance  which 
had  the  empiric  formula  C14H8N2S2,  and  to  which  he  assigned 
on  the  basis  of  several  syntheses  the  structure : 


oxalaminothiophenol  (2  :bis-benzothiazole  [M.P.  306]).  It  crys- 
tallizes from  alcohol  in  white  needles  although  the  solubility  is 
very  slight.  No  good  proof  of  its  structure  was  given,  however, 
for  several  years. 

Following  this  he  prepared  a  number  of  the  homologues  of 
this  compound,  using  the  dibasic  aliphatic  acids  and  ortho-amino- 
thiophenol.  Only  a  year  later  Hess,13  after  having,  prepared  the 
aminothiocresols,  became  interested  in  this  general  reaction,  and 
using  3  sulphydroxy  4  amino  toluene  contributed  several  new 
compounds  which  will  be  given  later. 

Interest  in  these  new  sulphur  compounds  now  became  quite 
general.  Two  years  after  the  work  just  described,  Tiemann 


and  Piest14  succeeded  in  preparing  the  "Rosenkorper"  by  a  new 
method,  the  fusion  of  phenylanilino  acetic  nitrile  which  they  hap- 
pened to  be  studying,  with  sulphur.  They  demonstrated  that 
the  reaction  proceeded  according  to  the  equation : 

C6H5CH(C6H5NH)CN  +  2S  =  C13H9NS  +  H2S  +  HCN 
and    identified   the    product    by    its    melting    point    and   ultimate 
analysis. 

Then  in  1886  P.  Jacobson15  published  the  first  of  a  series  of 
important  contributions  to  the  chemistry  of  the  benzothiazoles. 
Thiobenzaldehyde  had  already  been  prepared  by  Klinger16  and 
from  this  thiobenzanilide,  which  was  also  prepared  by  Leo17 
(and  later  by  Gatterman — vide  experimental  part),  by  heating 
with  aniline,  but  in  repeating  this  work  and  studying  the  prod- 
ucts of  the  reaction  (stilbene  and  thiobenzanilide)  Jacobson  found 
also  some  of  Hofmann's  "Rosenkorper."  The  only  explanation 
that  he  could  give  for  its  formation  was  that  of  oxidation  of  the 
thiobenzanilide,  and  to  test  the  validity  of  his  reasoning  he  oxi- 
dized a  portion  in  alkaline  solution  with  potassium  ferricyanide 
and  showed  that  about  60%  of  the  product  was  the  expected 
phenyl-benzothiazole.  A  new  method  of  synthesis  had  been  de- 
veloped, for  he  recognized  at  once  the  generalization  that  could 
be  drawn  from  this  experiment,  and  proceeded  to  prepare  the 
2  methyl-benzothiazole,  and  claimed  to  have  obtained  benzothia- 
zole  itself,  by  the  oxidation  of  the  corresponding  thioanilides, 
though  in  the  case  of  the  last  mentioned,  he  was  later  disputed 
by  Hofmann. 

Apropos  of  the  thioanilides  a  rather  curious  coincidence  may 
be  mentioned.  Leo,  in  a  disssertation  for  his  doctor's  degree  at 
Bonn,  1878,  under  the  title  of  thioanilides,  described  a  substance 
which  he  prepared  by  the  distillation  of  thiobenzanilid  in  the 
presence  of  air,  and  to  which  he  assigned  the  formula  C27H20N2S2. 
From  his  observations  of  the  properties  of  the  substance  it  was 
evidently  the  "Rosenkorper,"  and  if  his  analytical  work  had  been 
a  little  more  accurate,  and  he  had  been  able  to  appreciate  the 
significance  of  his  discovery,  the  credit  for  the  original  work  in 
this  field  would  have  gone  to  him,  for  his  work  appeared  several 
months  before  Hofmann's  first  paper. 

In  188718  Hofmann  published  some  further  work  on  the  chem- 
istry of  this  series.  He  treated  ortho-aminothiophenol  with  car- 
bon disulphide  expecting  to  find  a  derivative  of  thiocarbanilid, 
but  obtained  instead  a  body  whose  empiric  formula  was  C7H5NS2 
and  which  he  showed  readily  was  2-sulphhydrobenzothiazole  and 
could  be  prepared  from  chlorbenzothiazole  and  sodium  sulphy- 
drate.  By  oxidation  of  this  compound  he  made  a  2:2  benzo- 
thiazole  disulphide,  shining,  silvery  plates  from  benzol,  M.P. 
180°  (Jacobson  later  186°)  and  by  methylation  the  thioether, 
colorless  prisms  from  dilute  ethyl  alcohol,  M.P.  52°.  The  latter 
had  an  odor  resembling  that  of  benzothiazole  itself,  and  also  was 
quite  similar  to  the  ethoxy  derivative  already  made. 

10 


In  this  paper  he  further  developed  two  new  methods  of  syn- 
thesis which,  however,  do  not  admit  of  general  application,  by 
preparing  2  phenylaminobenzothiazole  by  heating  a  mixture  of 
anisyl  and  thioanisyl  mustard  oils,  synthesized  by  the  method  of 
Multhaiiser19  ;  and  by  preparing  the  oxymethenyl  base  by  dis- 
tillation of  the  urethane 

/NHC*?OCtH, 

C*S>H 

which  he  obtained  from  the  mercaptan  and  chlorcarbonic  ester. 
During  the  same  year  he  conducted  a  research  on  naphthylthia- 
zoles  and  prepared  a  number  by  methods  similar  to  those  already 
given.  (Listed  at  the  end.) 

No  very  satisfactory  proof  of  the  structure  of  these  compounds 
had  appeared  at  any  one  time,  though  taking  into  consideration 
all  the  methods  of  synthesis  which  had  been  developed  up  to 
this  time,  there  is  little  doubt  left  in  the  mind  of  even  the  most 
critical  reader.  In  1887,20  however,  Hofmann  published  a  sum- 
mary of  the  facts  leading  to  the  structural  formulae  for  the 
thiazoles,  using  as  a  case  in  point,  oxalaminothiophenol.  Hof- 
mann's  proof  of  the  structure  of  oxalaminothiophenol  may  be 
briefly  abstracted  as  follows  : 

1.  Its  empiric  formula  from  analysis  is  C14H8N2S2. 

2.  On  hydrolysis  it  yields  ortho-amino-thiophenol  and   oxalic 
acid  according  to  the  equation: 


C14H8N2S2  +  4HOH  =  2QH  +  H2C204     , 

XSH 

3.  It  may  be  synthesized  as  follows: 

(a)   By  leading  cyanogen  into  a  strong  solution  of  ortho- 
aminothiophenol 


/Z 

2C«,H4C         +  N=C  —  C  =  -  N  -  >  CuH.N.S,  +  2NH3 
NSH 

By  adding  the  mercaptan  to  an  alcoholic  solution  we 
obtain  amidin  as  a  first  product 

/S\       /NH. 


SH 

(b) 


(according  to  Hofmann)  which  upon  further  treatment  with  the 
mercaptan  yields  oxalaminothiophenol.    Amidin  has  two  hydrogen 

11 


atoms  which  are  easily  replaced  by  phenyl  groups  and  must  hence 
be  attached  to  nitrogen  atoms,  and  on  treatment  with  KOH  which 
would  hydrolyze  amides  gives  the  potassium  salt  of  an  acid  which 
upon  liberation  of  the  free  acid  breaks  up  into  methenyl  base. 
The  latter  may  be  synthesized  from  formanilid  and  sulphur,  from 
thioformanilid  by  direct  oxidation,  and  by  condensation  of  ortho- 
aminothiophenol  with  formic  acid,  all  of  which  in  consideration 
of  his  previous  work,  lead  to  the  structure  of  methenyl  base  as 
methenyl  base  as  yx  .CN 

CO* 

The  acid  must  then  have  been 

•s 


C-COOH 

amidin,  as  given  above,  and  the  original  base 


4.  Now  Bladin72  working  with  orthonitroanilin  had  prepared 
an  analogous  series  of  compounds  where  the  sulphur  atom  is  re- 
placed by  an  imido  group,  and  had  assigned  a  similar  structure 
to  his  final  product,  although  he  arrived  at  somewhat  different 
ones  for  the  intermediate  amidin  and  acid,  and  the  formula  agreed 
also  with  the  work  of  Ladenburg  (see  previously)  and  others 
in  related  fields,  so  Hofmann  believed  his  formula  to  be  justified. 

At  the  same  time  hq  reviewed  the  work  of  Jacobson,  and  con- 
tradicted the  latter's  statement  that  he  prepared  benzothiazole  by 
the  oxidation  of  thioformanilide  although  he  admitted  that  the 
ethenyl  base  could  be  obtained  in  this  way. 

At  the  end  of  this  paper  he  made  an  interesting  series  of  ob- 
servations and  described  a  few  preliminary  experiments  which 
should  be  a  very  fruitful  field  for  research,  and  yet  which  it  does 
not  appear  that  he  ever  followed  up,  although  he  promised  to  do 
so.  There  is  a  marked  resemblance  between  benzothiazole,  methyl 
benzothiazole,  quinolin  and  quinaldin,  as  can  be  seen  from  the 
formulae,  and  it  should  be  possible  to  obtain  from  these  two  a 
series  of  dyes  resembling  the  cyanins. 


0 


R  Rl 

Benzothiazole  Methylbenzothiazole  Typical  thiazole  cyanin 

12 


Qninolin  Quinaldin 


Rl 

Typical  eyanin 

In  the  cyanines  the  methyliodide  addition  products  are  used 
and  he  had  already  noted  that  the  methenyl  base  did  add  methyl 
iodide,  as  well  as  amyl  iodide.  In  a  preliminary  experiment  he 
condensed  the  two  thiazoles,  and  each  with  the  other  quinolin 
and  did  obtain  reactions  with  the  formation  of  dyes  but  he  did 
not  isolate  them  nor  proceed  further,  nor  does  it  appear  that 
any  further  work  has  been  done  on  these  compounds. 

All  of  this  work,  however,  had  had  very  little  influence  on 
commercial  chemistry.  Organic  sulphur  compounds  were  being 
manufactured  and  used  as  dyes  by  the  Germans,  but  they  were 
of  the  phenyl  sulphide  type  described  and  prepared  earlier  by 
Merz  and  Weith.  In  February  of  1888,  A.  G.  Green,21  chemist 
for  Brook,  Simpson,  and  Spiller,  an  English  dye  concern,  found 
that  by  fusing  paratoluidin  and  sulphur  he  obtained  two  sub- 
stances which  were  different  from  the  thiotoluidin  of  the  authors 
just  mentioned,  one  of  which  was  a  direct  cotton  dye  and  both 
of  which  were  primary  amines,  from  which  a  series  of  direct 
cotton  dyes  could  be  obtained  both  by  diazotization  and  coupling, 
and  by  substitution.  He  named  these  dehydrothiotoluidin  and 
primulin,  the  latter  because  it  dyed  cotton  directly  a  primrose 
(primula)  yellow,  and  prepared  a  number  of  derivatives,  the 
methylated  and  ethylated  bases,  sulphonic  acids,  and  several  azo 
dyes,  developed  a  process  for  producing  the  azo  color  directly 
on  the  fibre  using  primulin,  and  noted  that  the  diazonium  com- 
pound of  the  latter  was  affected  by  light22  to  such  an  extent 
that  it  would  only  couple  with  the  developer  satisfactorily  under 
certain  carefully  regulated  conditions.  Unfortunately,  he  neg- 
lected to  patent  his  work,  and  as  soon  as  his  firm  produced  them, 
and  the  Germans  became  interested,  they  found  this  out,  and  of 
course,  did  not  make  this  mistake.  Dahl  and  Company  imme- 
diately patented  a  process  practically  identical  with  Green's 
(D.R.P.  35790)  arid  all  of  the  important  work  which  followed 
was  covered  by  German  patents. 

P.  Jacobson23  took  up  this  topic  the  following  year  and  after  a 
brief  review  of  the  patent  literature,  and  of  the  earlier  work  of 
Merz  and  Weith,  Krafft,  and  Truhlar,24  he  developed  a  better 
synthesis  of  dehydrothiotoluidin  and  primulin  from  the  same 
starting  materials,  using  a  hydrochloric  acid  extraction,  and  sub- 

13 


sequent  crystallization  from  alcohol  as  his  method  of  purification. 
He  described  dehydrothiotoluidin  as  crystallizing  in  colorless  nee- 
dles, M.P.  190°-191°,  and  also  prepared  the  phenol,  colorless 
needles  from  alcohol  M.P.  256°,  and  the  acetyl  derivative  of  this, 
M.P.  132°,  crystallizing  from  alcohol  in  colorless  needles. 

During  the  same  year  Gatterman25  investigated  the  reaction  and 
showed  that  dehydrothiotoluidin  was  different  from  the  thiotol- 
uidin  of  Merz  and  Weith,  although  Dahl  and  Company's  origi- 
nal patent  described  it  as  such,  but  his  work  was  not  at  all  en- 
lightening from  a  structural  standpoint.  He  did  make  two  impor- 
tant contributions,  however — he  noted  that  dehydrothiotoluidin 
formed  a  dibrom  addition  product  in  glacial  acetic  acid  solution, 
although  he  did  not  isolate  the  product,  and  suggested  naphtha- 
lene as  a  solvent  from  which  primulin  could  be  crystallized  for 
purification.  He  also  investigated  the  action  of  sulphur  on  the 
other  toluidins. 

The  work  of  Anschiitz  and  Schultz26  which  appeared  at  the 
same  time  was  vastly  more  important  commercially  for  a  great 
number  of  patents  sprang  up  from  the  small  space  of  this  paper 
as  a  resting  place.  They  studied  the  action  of  sulphur  on  a  num- 
ber of  aromatic  amines  with  the  following  results : 

Starting  Material 
1.  P-toluidin 

acetyl  derivative  of 


Product 

Dehydrothiotoluidin 
CI4H12N2S 


M.P. 

191° 

225° 


Solvent 


Form 


Dehydrothioxylidin 


C16H16N2S 


2.  Amido  w-xylol 
acetyl  derivative  of 
Noted  the  formation  of  a  dibrom  addition  product. 


107C 
227C 


3.  Amido  />-xylol 


Dehydrothioxylidin 


rotoxy 
H  .NS 


acetyl  derivative  of 
Also  forms  a  bromine  addition  product.. 


4.  Pseudo-Cumidin 


C18H20N2S. 


C18H20N2S 


144C 
212C 

183C 
125C 


EtOH  Yellow 
needles 

EtOH  Yellow 
prisms 

EtOH  Yellow 
prisms 

EtOH  White 
needles 


EtOH      Yellow 
needles 


Benzol     Small 
yellow 
crystals 

EtOH      Yellow 
needles 


Up  to  this  point  the  structure  of  the  compounds  had  not  been 
considered  except  by  Green,  who  assigned  to  the  dehydrothioto- 
luidin on  very  little  evidence,  the  structure 


H 


which  is   not   accepted  at   present.      Gatterman   and   Pfitzinger5 

14 


now  took  up  the  problem.     In  his  previous  article  just  cited,  he 
had  prepared 


M.P.  123°,  by  removing  the  amino  group  from  dehydrothioto- 
luidin,  and  he  now  showed  that  it  was  a  member  of  the  benzo- 
thiazole  group  and  was  identical  with  the  product  previously 
prepared  by  Hess28  from  one  of  the  aminothiocresols  and  benzoyl 
chloride.  To  prove  this  he  synthesized  it  from  thiobenzotolu-idid 
by  the  method  of  Jacobson  and  proved  all  three  products  to  be 
the  same.  By  hydrolysis  he  then  split  the  two  substances  and 
showed  that  they  gave  the  expected  acids  and  aminothiocresol. 
From  this  he  concluded  that  .dehydrothiotoluidin  was  formed  by 
this  reaction 


and  had  the  structure  given. 

The  work  on  primulin  was  not  quite  as  satisfactory,  as  it  led 
to  two  conclusions  between  which  the  difficulties  of  purifying  the 
primulin  prevented  them  from  choosing.  It  may  be  considered 
to  be  formed  from  two  moles  of  dehydrothiotoluidin  similarly 
to  the  latter  itself  which  would  give  the  formula 


or  from  one  mole  each  of  dehydrothiotoluiddin  and  paratoluidin 
which  would  indicate  it  to  be  : 


From  1885  to  1890  a  great  deal  of  work  was  accomplished  in 
the  thiazole  field  ;  Hantsch  and  Weber,29  and  Mohlar30  and  Krohn 
prepared  the  methenyl  bases,  the  latter  from  methyl  and  dimethyl 
anilin  and  sulphur,  while  several  syntheses  of  the  Rosenkorper 
were  accomplished,  from  benzalanilin,  and  benzyl  anilin  by  Zieg- 
ler31  and  Wallach.32  Jacobson's  original  work  on  the  action  of 
oxidizing  agents  in  alkaline  solution  on  the  thioanilides  has  al- 
ready been  mentioned,  and  he  published  a  number33  of  articles 
on  this  reaction  by  himself  and  in  collaboration  with  Ney  ;  as 
well  as  on  the  other  reaction  he  had  discovered,  namely,  that  of 
carbon  disulphide  on  oxyazo  linkings  to  produce  thiobenzothia- 

15 


zoles,  while  from  2  thiazole  mercaptan  by  treatment  with  aniline, 
KalkhofT,34  and  Jacobson,35  separately,  and  the  latter  and  Schenke 
(just  given)  had  made  phenylaminobenzothiazole. 

In   1891   Jacobson  and   Frankenbacher36  prepared  several  new 
compounds  by  treating  jnustard  oils  with  sulphur. 


°Q£* 


N^ 

M.P.  240°  small  colorless  crystals  from  alcohol. 
2. 


M.P.    194°,   crystallizes   from  benzol  and  reacts  with  HgCU  in 
alcoholic  solution. 
3. 


colorless  needles  from  alcohol  M.P.  232 
4. 


oxxxo 


white  needles  from  CHC13  M.P.  180°. 

5. 

s\ 

C-S-CH. 


CO: 


colorless  needles  from  alcohol  M.P.  74°. 

6.  Phenylaminobenzothiazole    picrate,    rosettes    from    alcohol, 
M.P.  222°. 

7.  Phenyl-acetamino  benzothiazole,  colorless   needles   from  al- 
cohol, M.  P.   167°. 

All  are  odorless. 

Gatterman  and  Neuberg"  in  1891  worked  out  a  synthesis  of 
dehydrothiotoluidin  from  thioparanitrobenztoluid  following  out 
the  general  method  of  Jacobson,  preparing  in  the  course  of  the 
procedure  6  methyl-para-nitrophenyl-benzthiazole  but  did  not  de- 
scribe any  of  its  properties.  This  was  more  interesting  from  a 
theoretical  than  a  practical  standpoint,  as  the  synthesis  involved 
a  large  number  of  steps  and  much  material  was  lost  in  the  course 
of  the  reaction. 

Research  in  the  field  now  had  reached  the  point  where  investi- 
gation led  to  the  discovery  only  of  new  compounds  rather  than 

16 


of  general  reactions  for  the  preparation  of  the  thiazoles.  O.  Kym38 
prepared  some  of  these — 6  amino,  2  phenyl-benzothiazole,  yellow- 
green  leaves,  alcohol,  M.P.  202°  ;  the  acetyl  derivative  of  this 
compound  white  needles  from  alcohol,  M.P.  192°-193°  ;  6  amino- 
2  para-aminophenyl  benzothiazole,  yellow  needles  from  alcohol, 
M.P.  237°-238° ;  and  the  diacetyl  derivative  of  this,  reddish- 
needles  from  alcohol,  M.P.  272°-273°.  In  1896  Lauth39  pre- 
pared oxalaminothiophenol,  two  dinitro,  and  diamino  derivatives 
whose  structures  he  did  not  determine,  and  a  number  of  azo 
dyes  from  the  latter,  while  subsequently  other  special  methods  for 
the  preparation  of  Rosenkorper  were  developed  among  which  may 
be  mentioned  that  of  Voswinkel40  from  benzoyl  phenylhydrazine 
and  sulphur,  and  Wheeler,41  from  orthoamino-thiophenol  and  benz- 
imido  methyl  ether,  while  Schmidt42  prepared  6  dimethylamino 
benzothiazole  from  dimethyl-paraphenylene-diamine  thiosulphonic 
acid  by  condensation  with  formaldehyde  and  oxidation  of  the 
product  with  nitrous  acid.  Reissert43  also  did  some  work  on  the 
benzothiazoles,  but  did  not  contribute  anything  new  or  interesting. 
As  has  already  been  noted,  from  a  commercial  standpoint,  the 
most  important  compounds  of  this  group  are  the  so-called  anhydro- 
bases  which  are  obtained  by  the  direct  fusion  of  aromatic  amines 
with  sulphur,  although  perusal  of  the  patent  literature  shows 
that  almost  all  of  the  phenyl  benzothiazole  amines  that  have 
been  prepared  have  also  been  patented.  The  basic  patents  in 
the  dye-field  are  those  founded  upon  the  original  work  of  Green 
and  that  of  Anschiitz  and  Schultz,  and  all  may  be  classified  ac- 
cording to  the  particular  base  with  which  they  deal,  into  groups 
as  follows : 

1.  Mono  or  diamino  derivatives  of  2  phenyl  benzothiazole,  or 
2  phenyl  alpha  or  beta  naphthiazole.     These  are  not  very  impor- 
tant and  there  are  comparatively  few  patents  dealing  with  them. 

2.  Dehydrothiotoluidin,  6  methyl  2  para-aminophenyl  benzothi- 
azole which,  as  has  already  been  noted  is  the  most  important  of 
all,  and  a  large  number  of  patents  deal  with  its  preparation  as 
well  as  that  of  its  derivatives.     The  experience  of  different  con- 
cerns  which  have  manufactured   this  base  appears  to  have  dif- 
fered, as  may  be  readily  seen  from1  a  perusal  of  the  patent  litera- 
ture.44    The  main  difficulty  has  been  the  separation  of  the  prin- 
cipal product  from  the  primulin  simultaneously  formed,  a  problem 
which  has  not  been  satisfactorily  solved  although  it  can  be  done 
by  a  vacuum  distillation  of  the  fusion  mixture,  or  by  means  of 
the  difference  in  solubility  of  the  ammonium  salts  of  the  sulphonic 
acids  of   the  two   bases   as   described   by   Noetling45   and   in  the 
patent  just  given  (the  method  was  discovered  by  Hall  in  1889). 
For  the  preparation  of  some  of  the  thioflavins  the  sulphonic  acids 
are  undesirable,  so  this  method  has  a  serious  objection,  as  up  to 
date  it  has  not  been  possible  to  regenerate  dehydrothiotoluidin 
from  its  ammonium  sulphonate.46 

From  the  practical   side  the  application  of  the  dyestuff  is  as 

17 


important  as  its  preparation,  and  some  of  the  methods  of  sub- 
stantive cotton  dyeing  as  applied  to  primulin  are  discussed  by 
Haller,47  while  in  the  experimental  part  of  this  paper  an  adapta- 
tion of  the  Badische  method  which  works  fairly  well  for  labora- 
tory purposes,  is  given. 

3.  Dehydrothioxylidins,  of   which  the  commercially  important 
one  is  the  meta  compound 


'CH,  CH3 

prepared  as  mentioned  above  by  Anschiitz  and  Schultz,  and  de- 
scribed in  the  Bayer  Patent  already  given. 

4.  Dehydrothiopseudocumidin,  also  prepared  by  Anschiitz  and 
Schultz  and  covered  by  the  Bayer  patent,  which,  however,  does 
not  mention  which  of  the  two  isomers  is  meant — 

./sv 


5.  6-Para-aminophenyl  dehydrothiotoluidin,  prepared  from  ben- 
zidine  and  paratoluidine  and  the  corresponding  tolidine  compound, 
covered    by   several   patents   which   may   be    found   in   the   third 
volume  of  Friedlander. 

6.  6-6    Bisdehydrothiotoluidin,    prepared    also    from    benzidine 
and  paratoluidin,  and  the  corresponding  tolidine  compound,  which 
are  really  further  condensation  products  of  thosd  in  group  5. 

7 .  Bases  of  unknown  or  uncertain  structure,  such  as  primulin, 
the  chromins,  etc. 

From  these  seven  groups  a  large  number  of  dyes  have  been 
made  which  fall  more  or  less  naturally  into  subdivisions :  ( 1 ) 
Those  bases  which  are  themselves  direct  colors  on  cotton,  as  for 
example,  primulin  and  chromin ;  (2)  alkylated  bases,  or  alkylated 
and  sulphonated  bases  such  as  thioflavins ;  (3)  substituted  bases, 
nitro  derivatives,  etc.,  which  are  comparatively  few,  although 
nitro  derivatives  of  dehydrothiotoluidin  have  been  made  and  used 
as  dyes;  (4)  oxidation  products  like  naphthamine  yellow  pro- 
duced by  the  action  of  bleach  on  dehydrothiotoluidin,  and  (5) 
azo  dyes  which  are  by  far  the  greater  majority,  and  can  be  con- 
veniently subdivided  into  monoazo  and  bis-azo  compounds,  and 
both  of  which  are  represented  in  larger  numbers. 

The  colors  of  these  dyes  are  in  the  main  confined  to  the  red- 
yellow  end  of  the  spectrum,  although  in  the  derivatives  of  groups 
5  and  6  some  blues  and  greens  are  found.  A  series  of  greens 
may  also  be  obtained  by  coupling  diazotized  dehydrothiotoluidin 
with  the  naphthyl-amine  sulphonic  acids,  rediazotizing  and  treat- 
ing with  dioxy  naphthalene  disulphonic  acids.  It  is  interesting 
to  note  in  passing  that  while  primulin  can  be  diazotized  on  the 
fibre  as  was  shown  by  Green  in  his  original  work,  this  process 

18 


is  not  possible  with  dehydrothiotoluidin.  These  dyes  are  all  direct 
substantive  ones  for  cotton,  are  reasonably  fast  to  acid,  alkali, 
and  bleach,  but  as  has  been  noted  by  all  the  workers  in  the 
field,  only  moderately  so  to  light,  a  thing  which  of  course,  reduces 
materially,  their  value. 

This  fact  brings  up  a  rather  interesting  point  in  connection 
with  structural  relationship  of  organic  compounds.  The  indigoid 
and  thioindigoid  dyes  are  amongst  the  fastest  of  all  toward 
light  and  owe  a  great  deal  of  their  commercial  importance  to 
this  fact,  as  well  as,  of  course,  to  the  wide  variety  of  colors 
that  can  be  obtained  from  them,  particularly  in  the  case  of  the 
latter.  There  is  a  rather  close  genetic  relationship  between  some 
of  the  thiazoles  and  the  corresponding  compounds  in  the  indigo 
series  as  may  be  seen  at  a  glance  from  comparison  of  the  accepted 
structural  formulae  : 


Inrtoxyl  Thioindoxyl  Benzothiazole 

(Thionaphthene) 


Indigo  T'hioindigo  Oxalamido  thiophenol 

Benzo-thiazole  may  be  regarded  as  derived  from  indoxyl  by 
replacement  of  the  carbonyl  group  with  a  sulphur  atom  and  re- 
moval of  the  two  hydrogen  atoms,  and  oxalamido-thiophenol  as 
bearing  a  corresponding  relationship  to  indigo.  As  already  men- 
tioned, it  has  been  observed  by  several  workers  that  the  thiazoles 
form  dibrom  addition  products,  and  from  similar  reactions,  we 
should  expect  the  compound  which  Gatterman  did  not  investi- 
gate, to  have  the  formula 


and  to  be  reduced  to 


OS 


ocv 

\/^^  z 


H 

which  would  make  it  resemble  indoxyl  still  more  closely,  and 
then  reasoning  along  the  same  lines,  we  should  be  able  to  obtain 
the  analagous  reduced  oxalamido-thiophenol  both  by  reduction  of 
the  bromine  addition  product  which  has  not  been  made,  and  by 
oxidation  of  the  postulated  dihydro-methenyl  base.  If  the  ac- 

19 


cepted  view  of  the  cause  of  the  color  of  the  indigoid  dyes  is 
correct,  we  should  not  expect  the  compound  to  be  a  dye. 


APPENDIX  TO  THE  HISTORICAL  REVIEW 

1.  Friedlander  devotes  a  chapter  of  each  volume  of  his  work 
to  patents  dealing  with  sulphur  dyes,  most  of  which  refer  to  the 
so-called  anhydro  bases,  and  the  large  majority  of  them  are  de- 
scriptive of   azo   or   bis-azo  dyes.     Among  the  substances   with 
which  dehydrothiotoluidin  has  been  diazotized  and  coupled,  may 
be  mentioned  by  way  of  example :    salicylic  acid ;  beta  naphthol ; 
beta  naphthol  alpha  or  beta  monosulphonic  acids;  phenols  and 
cresols;    itself,    primulin,    and    their    sulphonic    acids;    tetrazo- 
diphenyl  or  tolyl ;  napthionic  acid ;  ammonia ;  metatolylene  dia- 
mine;   beta   naphthylamine    sulphonic   acids;   resorcin;    oxynaph- 
thoic  acid;  naphthol  disulphonic  acids;  dyes  such  as  chrysoidin 
and    Bismark    Brown;    alpha    naphthylamine    sulphonic    acids; 
Cleve's  acids  further  diazotized  and  coupled  with  compounds  al- 
ready given;   and  the  aminonaphthols   and  their   mono   and   di- 
sulphonic acids  and  ethers. 

2.  To  substantiate  the  conclusions  arrived  at  regarding  the  sec- 
ond and  third  purposes  of  this   research,   the   following  partial 
list  of  compounds  which  have  been  prepared  by  previous  workers 
together  with  their  properties,  in  addition  to  those  already  men- 
tioned and  others  which  will  be  described,  is  given.     These  are 
all  benzothiazole  derivatives  and  merely  the  substituting  groups 
and  their  positions  are  indicated  for  the  simpler  ones. 

Groups 
benzothiazole 

2  chlor  M.P 

(?)    nitro  2  chlor 
2  hydroxy 
2  ethoxy 
2  acetoxy 
2  amino 
2  phenylamino 
2  methyl 
2  ethyl 
2  butyl 

S2  dibenzothiazole  ethane 
p  2  dibenzothiazole  benzene 
2  oxymethyl 
2  benzyl 

2  orthohydroxyphenyl 
S-phenyl  benzothiazole  ethane 
6  methyl 
2,  6  dimethyl 
6  methyl  2  phenyl 
2  phenyl  naphthiazole 
naphthiazole 
2  methyl  naphthiazole 

oxalaminoalphathionaphthol                        300°  yellow 

oxalamino  betathionaphthol  yellow 


M.P. 

210° 
24°  B.P.  248° 

192° 

139° 
25° 
60° 

129° 

159° 

B.P.  238° 
B.P.  252° 
Not  found 

137°    ' 

112° 

176° 


129° 
111° 

M.P.  15°  B.P.  255° 
No  data 

125° 
100—101° 

45° 

No  data 
300° 

20 


Odor  Color 

aromatic  none- white 

«  « 

none 

aromatic 

none  " 


aromatic 

not  given 
none 


none 

aromatic 

none 


EXPERIMENTS 
4          PART  A  —  BENZOTHIAZOLES 

1.  Oxalamino-thiophenol 

In  order  to  become  familiar  with  the  technique  of  the  prepara- 
tion of  these  compounds,  this  synthesis  was,  attempted  as  a  start- 
ing point,  since  it  involves  a  sulphur  fusion  which  may  be  con- 
sidered typical.  300  g.  of  acetanilide  was  heated  with  180  g. 
of  powdered  roll  sulphur  following  the  directions  of  A.  W. 
Hofman.48  The  weight  of  the  melt  at  this  point  was 
282  g.,  which  was  then  treated  according  to  the  directions  of 
Lauth49  for  extracting  the  pure  compound.  60%  sulphuric  acid, 
by.  weight,  extracted  only  140  g.  of  the  melt  corresponding  to  a 
50%  yield  against  60-70%  as  given  by  the  original  article.  Crys- 
tallization from  boiling  aniline  yielded  a  colored  product,  and  as 
the  solubility  in  ethyl  alcohol  is  less  than  1  g.  per  100  c.c.  and 
it  is  equally  or  more  insoluble  in  ether,  nitrobenzene,  aniline, 
amyl  alcohol,  amyl  acetate,  and  mixtures  of  these,  it  was  decided 
that  purification  by  other  methods  than  sublimation  was  imprac- 
ticable. Sublimation  of  75  g.  yielded  7  g.  of  white,  odorless 
needles,  melting  at  304°  (Unc.),  which  was  then  recrystallized 
from  a  large  volume  of  ethyl  alcohol.  The  final  yield,  calculated 
back,  was  less  than  5%  of  the  acetanilid  used,  and  was  con- 
siderably less  than  that  given  by  either  of  the  previous  investi- 
gators. 

The  extreme  minuteness  of  the  yields  proved  to  be  a  regular 
occurrence  in  all  similar  experiments  and  this,  as  well  as  the 
difficulty  in  obtaining  the  intermediates  required,  was  a  continual 
source  of  vexation  and  a  serious  handicap  to  the  progress  of 
the  work.  For  this  reason  the  syntheses  in  each  case  are  given 
fairly  completely  to  save  time  wherever  it  may  be  necessary  or 
desirable  to  duplicate  or  continue  the  work.  The  yields  de- 
scribed in  this  dissertation  have  all  been  actually  obtained  and 
can  be  duplicated  by  fairly  careful  manipulation. 

In  accordance  with  the  first  and  third  purposes  of  this  research, 
it  was  considered  desirable  to  prepare  a  homologue  of  the  "Rosen- 
korper"  and  to  determine  whether  it  would  exhibit  an  odor  resem- 
bling that  of  the  interesting  substance  obtained  by  Hofmann. 
With  all  the  methods,  previously  enumerated,  available,  it  was 
decided  to  attempt  the  synthesis  of  2-paratolyl-benzothiazole  which 
if  successful,  would  be  a  new  contribution  to  the  chemistry  of 
the  group,  by  the  original  method  of  Hofmann,  which  should 
proceed  as  follows  : 


Paratolanilide  was  required  as  a  starting  material  and  as  it  was 

21 


not  available,  the  synthesis  was  perforce  accomplished  from  para- 
toluidin. 

2.  Paratoluyl  Nitrilc 

This  compound  was  made  following  the  directions  of  Gatter- 
man50  and  of  Fisher.51     The  reaction  proceeds  as  described  and 
the  yields  and  melting  points  coincide  with  the  accepted  ones. 
3.  Pdratoluic  Acid 

Prepared  according  to  the  directions  of  Gatterman  and  Fisher 
as  just  given.     Yield  and  M.P.  were  as  recorded. 
4.  Paratoluyl  Chloride 

As  first  attempted,  a  method  adopted  from  Gatterman's50  prep- 
aration of  benzoyl  chloride  was  employed.  The  reaction  does 
not  proceed  satisfactorily  and  after  two  trials  it  was  discarded. 

The  compound  was  synthesized  by  the  method  of  Frankland 
and  Wharton52  (see  also  F.  and  Aston)  and  the  yield  was  55-60% 
of  product  boiling  from  182°  C.-1850  C.  at  a  pressure  of  260  m.m. 
5.  Paratolanilide 

The  literature  furnishes  a  number  of  methods  for  this  synthe- 
sis by  Wegerhoff,53  Bruckner.54  Fischli/'5  and  Leuckhardt,56  and 
the  observed  melting  points  vary  from  139°  C.  (Fischli)  to  145° 
C.  (Leuckhardt). 

Since  paratoluyl  chloride  was  available  from  the  previous  syn- 
thesis, the  method  of  Fischli  was  selected  and  modified. 

In  a  one  liter  flask,  dissolve  15  g.  (18  c.c.)  of  freshly  dis- 
tilled aniline  in  200  c.c.  of  water-  and  alcohol-free  ether.  From  a 
dropping  funnel  add  slowly  with  good  stirring  25  g.  of  paratoluyl 
chloride.  The  reaction  proceeds  smoothly  according  to  this  equa- 
tion: 

CH3C6H4COC1  +  C6H5NH2  =  CH3C6H4CONHC6H5  +'HC1 
the  product  separating  out  at  once  as  a  fine  white  precipitate. 
Evaporate  off  the  ether,  or  better,  distill  off  on  a  water  bath,  and 
dissolve  the  residue  in  the  least  amount  of  50%  ethyl  alcohol,  in 
which  the  solubility  is  about  5  g.  per  100  c.c.,  by  warming.    Allow 
to  cool,  filter  by  suction,  and  wash  with  cold  water.     The  yield 
is  practically  quantitative  and  the  purity  of  the  product  is  satis- 
factory for  most  purposes.     On  recrystallization  from  ethyl  al- 
cohol it  appears  in  shining  white  plates,  M.P.  145°  C.  (cor.). 
6.  2-Paratolyl  Benzothiazole  (A) 

The  first  attempt  to  prepare  this  compound  was,  as  has  already 
been  mentioned,  according  to  Hofmann's  first  general  method, 
the  fusion  of  the  anilide  with  sulphur.57  A  mixture  of  two  parts 
by  weight  of  paratolanilide  and  one  part  of  powdered  roll  sul- 
phur was  placed  in  a  flask  equipped  with  a  reflux  air  condenser, 
and  kept  at  a  temperature  of  290°  to  300°  C.  pfor  two  hours  on 
an  oil  bath.  At  the  end  of  this  time  the  melt  was  poured  into 
a  beaker,  allowed  to  solidify,  and  powdered.  The  weight  of  the 
fusion  mixture  at  this  point  was  1.5  to  1.6  parts  in  several  experi- 
ments, and  was  dark  brown  in  color.  It  was  extracted  repeatedly 

22 


with  100  c.c.  portions  of  concentrated  hydrochloric  acid  (39% 
HC1  by  weight,  specific  gravity,  1.2)  and  the  liquid  extract 
diluted  with  water,  but  no  precipitate  formed.  On  neutralization 
with  sodium  carbonate  and  long  standing,  a  small  amount  of 
yellow  material,  insufficient  to  purify,  was  deposited,  and  a  solu- 
tion of  this  in  alcohol  and  in  concentrated  hydrochloric  acid  gave 
a  yellow  precipitate  with  1%  gold  chloride  solution,  a  reaction 
which  is  characteristic  of  these  bases.  Alcohol  and  ether  extrac- 
tions of  the  melt  gave  similar  results,  and  it  is  probable  that  the 
yield  of  the  desired  substance  in  the  reaction,  is  positive,  but 
certainly  less  than  \%. 

It  was  thought,  however,  that  the  direct  fusion  of  the  two 
substances  might  have  been  responsible  for  the  low  yield,  due  to 
too  powerful  oxidation  and  consequent  charring,  and  accordingly 
the  addition  of  naphthalene  as  a  diluent  was  next  tried.  The 
melts  were  made  up  as  follows  : 

Paratolanilide  12  g. 

Naphthalene  12  g. 

Roll  Sulphur  6  g. 

according  to  the  method  described  later  for  dehydrothiotoluidin. 
They  were  heated  for  two  hours  starting  at  160°  and  ending 
at  200°.  At  the  end  of  the  first  hour  a  marked  color  change  to 
yellow  occurs,  but  the  desired  substance  was  not  found  in  the 
final  mixture. 

Hofmann's  method  for  preparing  the  desired  compound  having 
failed,  it  was  next  decided  to  attempt  its  synthesis  analagously 
to  the  method  by  which  Jacobson58  had  obtained  the  "Rosen- 
korper,"  for  which  the  reaction  should  be  in  this  case  : 

/s\ 

CsHsNH-CS-C6H4CH3-t*C6H4^       ^C-  C6H4-  CH3+H20 


Thioparatolanilide  was  required  as  a  starting  substance  and  as 
this  was  not  available,  it  was  again  necessary  to  prepare  a  num- 
ber of  intermediates. 

7.  Thiocarbanilide 

Prepared  from  aniline  and  carbon  disulphide  according  to 
Gatterman.50 

8.  Phenyl  Mustard  Oil 

This  was  made  from  thiocarbanilide  as  described  by  Gatter- 
man.50 

9.   Thioparatolanilide 

This  compound  was  synthesized,  by  the  method  of  Gatterman50 
whose  method  is  simpler  than  that  of  Leo,  which  has  already 
been  mentioned  in  the  introduction.  Since  the  substance  was 
required  in  fairly  large  quantities,  it  was  found  necessary  to 
modify  the  original  method  somewhat,  as  it  is  undesirable  to 

23 


use  amounts  much  larger  than  those  in  the  above-mentioned  paper, 
because  of  the  tendency  of  the  aluminum  chloride  to  cake,  with 
an  accompanying  reduction  in  yield.  It  is  preferable  to  carry 
out  the  reactions  in  separate  vessels.  The  ensuing  directions  in- 
volve about  the  maximum  quantities  with  which  it  is  possible 
to  secure  satisfactory  results,  but  by  running  a  number  side  by 
side,  much  more  can  be  made  without  a  great  increase  in  the 
time  necessary,  and  with  very  good  yields. 

A  mixture  of  15  g.  of  phenyl  mustard  oil,  30  g.  of  toluene 
and  30  g.  of  aluminum  chloride,  (anhydrous)  is  allowed  to  stand, 
in  a  one  liter  flask  with  an  electric  stirrer,  on  a  water  bath  for 
two  hours,  and  then  to  complete  the  reaction,  is  left  over  night. 
Decompose  the  solid  reaction  product  carefully  with  ice  water, 
and  distill  off  the  unchanged  toluene  and  phenyl  mustard  oil  with 
steam.  On  more  than  one  run  this  may,  of  course,  be  done 
successively  with  the  same  apparatus.  The  residual  liquid  in  the 
flask  is  poured  into  a  beaker  and  deposits,  on  cooling,  a  solid 
which  consists  chiefly  of  the  anilide,  but  contains  some  alkali- 
insoluble  impurities.  Filter  off,  and  if  more  than  one  prepara- 
tion is  being  made,  unite  the  yields  at  this  point. 

Warm  the  solid  material  with  10%  KOH  using  300  c.c.  to 
each  run,  and  filter.  Extract  a  second  time,  using  150  c.c.  to 
each.  (The  solubility  of  the  anilide  is  about  9.2  g.  per  100  c.c. 
in  the  dilute  alkali  at  20°  C.)  Unite  the  filtrates  ^and  neutralize 
with  20%  sulphuric  acid.  Yield  is  80%  of  the  theory  and  the 
purity  is  sufficient  for  most  purposes.  (This  yield  may  be  cut 
to  40%  simply  by  using  double  the  quantities  directed.) 

Thioparatolanilide  may  be  recrystallized  from  ethyl  alcohol,  in 
which  the  solubility  at  the  boiling  point  is  about  30  g.  per  100 
c.c.,  in  which  it  gives  a  red  solution,  which  on  cooling,  deposits 
yellow  nedles  meltng  at  142°  C.  (cor.). 

10.  Paratolylbenzothiazole  (B) 

From  the  compound  just  described,  the  new  sulphur  base  was 
prepared  successfully  by  an  adaptation  of  the  method  of  Jacob- 
son.60 

In  a  liter  beaker,  dissolve  16  g.  of  thioparatolanilide  in  700  c.c. 
of  water  containing  60  g.  of  sodium  hydroxide.  (An  equal 
weight  of  potassium  hydroxide  can  be  used  with  the  same  re- 
sults.) It  is  necessary  to  warm  to  effect  solution.  Allow  to 
cool  to  room  temperature  and  add  227  c.c.  of  a  20%  solution 
(containing  45  g.  of  solute)  of  potassium  ferricyanide.  The  mix- 
ture becomes  milky  yellow  at  once.  Allow  to  stand  twenty-four 
hours  and  filter  off  the  resinous  precipitate. 

Extract  twice  with  150  c.c.  and  100  c.c.  of  concentrated  hydro- 
chloric acid  respectively,  filtering  through  asbestos  each  time.  The 
solid  becomes  a  bright  red  at  first,  on  addition  of  the  acid.  Mix 
the  extracts  and  drown  them  in  .ten  times  their  volume  of  water. 
After  extraction  all  but  a  small  amount  of  material  which  is  an 

24 


oil  below  100°,  but  solidifies  to  a  gummy  mass,  should  have  dis- 
solved. The  precipitate  on  the  addition  of  water  is  voluminous 
and  pale  yellow  in  color.  The  weight  is  60-75%  of  the  theory 
according  to  the  equation  given  above.  There  is  no  advantage 
in  neutralizing  the  acid  with  sodium  carbonate. 

Absolute  purity  requires  several  recrystallizations  from  alcohol, 
as  the  impurities  though  small  hi,  quantity  are  difficult  to  remove, 
which  finally  yields  it  in  colorless,  odorless  needles,  melting  at 
85°  C.  (cor.).  When  slightly  moist  with  alcohol,  the  new  base 
has  a  faint  odor  which  is  somewhat  suggestive  of  "Rosenkorper," 
but  its  intensity  is  so  small  as  to  be  barely  perceptible. 
Analysis- 

Calculated  for  C14HnNS  N=    6.22% 

*  =  j 

1  1  .  2-Phenylaminobensothiasole 
In  the  light  of  the  synthesis  just  given,  it  occurred  to  the 
author  that  the  2  phenylaminobenzothiazole  which  has  previously 
been  prepared  by  Hofmann  and  others,  should  be  formed  by  the 
oxidation  of  thiocarbanilid.  in  the  Jacobson  reaction,  according 
to  the  equation: 

N 


Accordingly  the  experiment  just  described  was  repeated,  using 
the  same  molecular  quantity  of  thiocarbanilid  instead  of  thiopara- 
tolanilide.  The  precipitate  which  formed  in  the  oxidation  mix- 
ture was  found  to  be  practically  insoluble  in  concentrated  hydro- 
chloric acid,  the  liquid  extract  on  dilution  with  water  deposit- 
ing only  a  trace  of  gray-white  substance  which  on  a  single  crys- 
talization  from  ethyl  alcohol  melted  at,  144.5°  C.  (cor.)  and  may 
have  been  the  desired  compound  but  the  amount  was  too  small 
to  identify.  The  residue  was  yellow  in  color  and  had  lost  very 
little  in  weight,  and  from  it  a  substance  soluble  in  alcohol,  from 
which  it  crystallized  in  yellow  needles  melting  at  237.5°  C.,  was 
isolated. 

At  the  end  of  one  of  his  papers,  Jacobson60  makes  a  brief  refer- 
ence to  having  tried  this  reaction,  and  mentions  carbanilid  as 
one  of  the  products,  the  other  being  an  amorphous,  insoluble 
material  that  was  not  investigated.  This  may  be  prepared  as 
follows  : 

Dissolve  by  heating,  18.0  g.  of  thiocarbanilide  in  800  c.c.  of 
water  to  which  has  been  added  60  g.  of  sodium  hydroxide.  All 
will  not  quite  dissolve.  Cool  and  add  a  solution  of  52  g.  of 
potassium  ferricyanide  in  260  c.c.  of  water.  Let  stand  24  hours, 
filter,  and  dry.  Residue  is<  yellow  in  color  and  weighs  16  g. 

Extract  with  150  c.c.  of  95%  ethyl  alcohol  by  heating.     Filter. 

25 


A  second  extraction  is  unnecessary.  The  residue  is  yellow,  weighs 
7  g.,  is  highly  insoluble  in  all  ordinary  solvents,  except  nitro- 
benzene, from  which,  however,  it  was  not  successfully  crystal- 
lized, and  is  evidently  the  product  mentioned  by  Jacobson.  After 
some  difficulty,  his  other  observation  was  also  verified.  The  fil- 
trate was  allowed  to  crystallize,  and  then  the  product  repeatedly 
crystallized  from  alcohol,  yielding  finally  a  substance  melting  only 
slightly  below  carbanilid  but  exhibiting  a  yellow  color  and  giv- 
ing a  qualitative  test  for  sulphur.  It  was  attempted  to  hydrolyze 
this  compound  using  30 %  aqueous  potassium  hydroxide,  and  20% 
alcoholic  potash  in  different  experiments.  Both  yielded  the  same 
substance,  which  appeared  in  white  shining  needles  on  recrystal- 
lization  from  ethyl  alcohol,  melted  at  238°  C.  (cor.),  were  free 
from  sulphur,  and  gave  the  bromine  addition  product  charac- 
teristic of  carbanilid.  (As  did  also  the  original  substance.)  Con- 
trary to  the  test  given  by  Mulliken61  carbanilid  is  apparently  not 
hydrolyzed  rapidly  by  alcoholic  potash  which  does,  however,  re- 
move the  sulphur-bear jng  jmpurity.  This  can  also  be  done  by 
shaking  the  original  material  with  alcohol  in  which  the  carbanilide 
dissolves  more  rapidly  and  leaves  a  small  amount  of  yellow  mate- 
rial, too  little  to  examine,  however,  at  the  bottom  of  the  vessel. 
The  extreme  insolubility  of  the  first  substance  made  impossible 
any  further  investigation  of  it. 

The  aniline  blues  and  reds  are  among  the  most  important  of 
the  triphenylmethane  dyes  and  have  been  prepared  in  a  number 
of  ways,  from  benzyl  chloride,  para  rosaniline  and  aniline,  di- 
phenyl  amine,  etc.,62  and  of  this  group  probably  the  best  known 
is  aniline  blue  itself,  to  which  the  structure 

(C6H0NHC0H4)2  :C  :C6H4  :N.C6H5.HC1 

is  ordinarily  assigned.  The  last  mentioned  synthesis  of  this  com- 
pound suggested,  that,  since  phenylaminobenzothiazole  contains  a 
secondary  nitrogen  group  and  is  structurally  closely  related  to 
diphenylamine,  it  would  react  similarly  in  the  Hausdorfer  reac- 
tion, yielding  upon  fusion  with  oxalic  acid,  a  substance  whose 
probable  structure  would  be 

(C7H4NS.NHC6H4)2  :C  :CBH4  :N  —  SNC7H4. 
Reasoning  by  analogy,  this  compound  should  be  a  direct  silk  dye 
and  probably  have  a  color  in  the  blue-green  region  of  the  spec- 
trum. 

As  has  been  previously  noted,  phenyl  aminobenzothiazole  has 
been  synthesized  by  a  number  of  methods  which  may  be  briefly 
summarized : 

(1)  From  phenyl  mustard  oil  and   phosphorus   pentachloride, 
followed  by  treatment  with  aniline,  by  Hofmanri.83 

(2)  From  anisyl   and  thioanisyl  mustard  oils  by  Hofmann.64 

(3)  By  Jacobson  and  Frankenbacher  from  phenyl  mustard  oil 
and  azo-benzene.65 

(4)  By  hydrolysis  of  the  dibrom  addition  product  of   thiocarb- 
anilid  with  sodium  carbonate,  by  Hugershofr'.66 

26 


Consideration  of  the  methods  available  led  to  the  selection  oi 
the  fourth  as  being  the  simplest  both  from  the  standpoint  of 
manipulation,  and  ease  in  obtaining  the  necessary  reagents,  for 
the  difficulty  in  preparing  starting  materials  was  a  continually 
vexatious  matter  in  the  course  of  this  research.  Accordingly 
the  compound  was  prepared  by  the  method  of  Hugershoff  which 
was  found  to  yield  the  amount  of  product  recorded  by  him,  in  a 
good  state  of  purity,  with  a  great  deal  of  unnecessary  labor, 
a  thing  which  in  almost  every  preparation  in  the  thiazole  field 
was  a  decided  handicap,  for  many  of  the  reactions  which  were 
met  with  during  this  work,  did  not  give  the  yields  which  the 
context  would  seem  to  indicate,  and  the  problem  of  purification 
is  always  a  peculiarly  difficult  one  because  of  the  number  and 
nature  of  the  by-products  of  the  reactions,  as  well  as  in  many 
cases  the  extreme  insolubility  of  the  principal  substance  in  most 
ordinary  solvents. 

2-Phenylaminobenzothiazole  is  a  colorless,  odorless  solid  crys- 
tallizing from  ethyl  alcohol  in  small  crystals,  melting  at  161°  C. 
(cor.).  As  its  physical  properties  as  well  as  the  chemical  and 
physical  properties  of  the  new  dye  differ  somewhat  from  those 
of  the  corresponding  substances  in  the  aniline  blue  reaction,  it- 
was  necessary  to  modify  the  procedure  in  order  to  apply  it  to 
the  case  in  hand. 

12.  Tri  (2  Anilinobenzothiazolyl)  Carbinol 

A  mixture  of  20  g.  of  phenylaminobenzothiazole  and  10  g.  of 
oxalic  acid  is  heated  to  170°  on  an  oil  bath  in  a  flask  equipped 
with  a  reflux  air  condenser  and  10  g.  more  of  oxalic  acid  is 
added  in  the  course  of  15  or  20  minutes.  The  temperature  of 
the  reaction  mixture  is  then  raised  to  190°  and  kept  there  for 
two  hours.  It  foams  at  first,  probably  due  to  decomposition 
of  the  acid,  but  at  the  end  of  the  time  remains  in  a  state  of  quiet 
fusion.  Pour  into  a  beaker  and  allow  to  cool  and  solidify. 

Grind  up  in  a  mortar  and  extract  twice  with  hot  water  to 
remove  the  excess  oxalic  acid.  The  water  acquires  a  slight  purple 
color  and  a  purple  mass  remains.  Dissolve  in  150  c.c.  of  boil- 
ing 96%  ethyl  alcohol  and  add  5  c.c.  of  concentrated  hydrochloric 
acid.  The  dye  will  not  crystallize  out  on  standing,  and  the  solu- 
tion is  evaporated  to  a  gummy  paste  to  which  is  added  40  c.c.  of 
ethyl  alcohol  and  a  solution  of  2.5  g.  of  sodium  hydroxide  in 
20  c.c.  of  ethyl  alcohol.  (The  last  two  steps  may  be  omitted  as 
is  obvious  on  consideration,  but  are  recommended  for  purifica- 
tion.) Heat  under  a  reflux  condenser  for  one  hour  and  allow  to 
stand  for  24  hours.  A  white  precipitate  settles  out  and  the 
supernatant  liquid  is  brown  in  color. 

Filter  and  neutralize  to  litmus  with  dilute  (1:1)  hydrochloric 
acid.  The  liquid  becomes  purple  as  the  neutral  point  is  approached 
and  a  small  amount  of  resinous  material  separates  out.  Filter 
this  off  and  reject  it. 

27 


The  filtrate  is  treated  with  double  its  volume  of  water  and 
allowed  to  stand  one  hour  before  filtering.  The  precipitate  ap- 
pears to  be  a  mixture  of  the  leuco  base  and  color  base  and  its  dry 
weight  is  19  g.  or  90%  according  to  the  reaction: 

3C13H10N2S+HA04=C40H26N6S,+3H20+CO 
The  melting  point  is  not  sharp,  but  is  below  100°. 

13.  Di-benzothiazolyl-Fuchsone-BenzothiazolyUniine 
The  leucobase  is  then  oxidized  to  the  dye  with  lead  peroxide 
by  the  method  of  Gatterman50  using  a  suspension  of  the  finely 
powdered  material  as  it  is  insoluble.  Heat  and  shake  the  solution 
for  15  minutes  and  filter  after  adding  the  sodium  sulphate  accord- 
ing to  his  direction.  Extract  the  precipitate  with  hot  ethyl  alcohol 
and  precipitate  with  water. 

The  new  dye  has  a  deep  purple  color  but  very  poor  tinctorial 
value,  dyeing  silk  only  a  pale  lavender  from  alcohol  solution  as  it 
is  insoluble  in  water.  This  is  probably  due  to  the  fact  that  appar- 
ently the  hydrochloride  is  unstable  and  is  hydrolyzed  by  water,  for 
a  qualitative  analysis  showed  C,  H,  N,  and  S,  but  no  chlorine. 
It  was  then  analyzed  for  nitrogen  according  to  the  method  of 
Fisher51  as  were  the  other  analyses. 
Calculated  for  C40H26N6S3  N=  12.24% 

N= 


14.  Sulphonation  of  the  Dye 

It  was  thought  that  the  poor  tinctorial  value  of  the  new  sub- 
stance might  be  due  in  part  to  its  neutrality  and  extreme  insolubil- 
ity, so  an  attempt  was  made  to  sulphonate  it  with  15%  fuming  sul- 
phuric acid.  The  sulphonation  mixture  was  diluted  with  water, 
neutralized  with  barium  hydroxide,  and  the  precipitated  barium 
sulphate  was  filtered  off.  The  resultant  yellow  solution  was  con- 
centrated and  allowed  to  crystallize,  depositing  pale  yellow  plates, 
but  as  the  hue  of  the  dye  appeared  to  be  destroyed  in  the  process, 
no  further  work  was  done  on  it. 

15.  Nitro-tolyl  Benzothiazole 

In  connection  with  the  second  and  third  purposes  of  this  inves- 
tigation, it  was  considered  desirable  to  prepare  some  of  the  de- 
rivatives of  the  paratolyl  benzothiazole  especially  the  nitro  ones, 
because  the  nitro  group  frequently  functions  as  an  odorophore, 
as  in  the  synthetic  musks  ;  and  the  amino  derivatives,  which  would 
be  isomeric  with  the  valuable  dehydrothiotoluidin  which  has  al- 
ready been  mentioned  a  number  of  times. 

The  nitration  of  paratolyl  benzothiazole  may  be  accomplished 
with  fuming  nitric  acid  or  a  1:1,  by  volume,  mixture  of  concen- 
trated sulphuric  and  nitric  acids.  The  best  procedure  for  mod- 
erate quantities  follows: 

In  a  small  flask  dissolve  2.5  g  of  paratolylbenzothiazole  in  10  c.c. 
of  concentrated  sulphuric  acid  and  add  10  c.c.  concentrated  nitric 

28 


acid.  The  solution  becomes  warm  at  once,  nitrogen  tetroxide 
is  evolved,  and  the  color  changes  from  yellow  to  reddish-brown. 
Heat  on  a  water  bath  for  one  hour.  Let  cool  and  pour  into  100 
c.c.  of  water.  A  bright  orange-yellow  precipitate  settles  out, 
which  on  drying  weighs  3  g.  The  colored  impurities  may  be 
removed  by  warming  on  a  water-bath  with  about  50-80  c.c.  of 
ethyl  alcohol,  and  the  residue  can  then  be  dissolved  in  50  c.c.  of 
hot  toluene,  which  on  cooling  deposits  the  mono-nitro  derivative 
in  pale  cream-colored,  odorless  crystals,  M.P.  219.5°  C.  (cor.). 

Calculated  for  C14H10CXN2S        N  =    10.38% 

HISS? 

The  nitration  proceeds  smoothly  and  quantitative  yields  accord- 
ing to  the  equation 

C^H^NS  +  HNO3  =  C14H10O2N2S  +  H2O 
may  be  obtained  from  any  weights.     Toluene  is  a  remarkably 
good  solvent  for  purification,  as  the  difference  in  solubility  with 
temperature  is  strikingly  great. 

16.  Aminotolyl  Benzothiazole 

The  nitro  derivative  was  then  reduced  using  zinc  or  tin  and 
hydrochloric  acid  according  to  the  method  of  Gatterman.50  The 
amine  forms  an  addition  product  with  the  metallic  salts  from 
which  it  is  a  little  difficult  to  remove  the  metal,  and  may  be  crys- 
tallized from  ethyl  alcohol,  amyl  alcohol,  or  toluene,  none  of 
which  are  good  solvents  as  the  substance  is  quite  insoluble,  but 
the  last  is  the  best  of  the  three,  and  yields  the  base  in  small 
brown  crystals,  which  are  much  lighter  in  color  on  pulverization 
and  melt  at  229°  C.  (cor.).  Amyl  alcohol  and  toluene  solutions 
exhibit  a  bluish-green  fluorescence  which  is  characteristic  of  most 
of  the  benzothiazoles. 

Calculated  for  C14H12N2S  N=    11.67% 


17.  Azo  Dyes  from  Amino  Paratolyl  Benzothiazole 

Amino  paratolyl  benzothiazole  is  not  a  dye  but  can  be  diazotized 
on  the  fibre  and  coupled  with  the  usual  materials  and  yields  a 
series  of  direct  cotton  colors.  This  was  done  according  to  the 
method  which  will  be  described  later,  with  the  results  noted  in 
the  table.  With  the  amines  as  couplers,  the  developer  was  made 
up  as  a  2%  solution  by  weight,  using  sufficient  glacial  acetic  acid  to 
dissolve  them,  and  after  the  cloth  was  immersed,  the  bath  was 
neutralized  with  10%  NaOH,  thus  precipitating  the  dye  out  in  the 
fibres  of  the  material.  Other  acids  do  not  appear  to  give  satisfac- 
tory results. 

29 


TABLE 
Base  diazotized  and  coupled  with : 

Coupler 

1.  Phenol 

2.  Aniline 

3.  />-Cresol 

4.  Para-toluidin 

5.  ^-naphthol 

6.  Alpha-naphthylamine 

7.  5-naphthylamine 

8.  Resorcinol 

9.  Benzoylene  urea 
(2)    diazotized 


10. 
11. 
12. 
13. 
14. 
15. 
16. 
17. 


(2) 

(2) 

(12) 

(6) 

(6) 

(7) 

(7) 

18.  base 

19.  " 

20.  (6) 
(7) 
(6) 


21. 
22. 


-f-  resorcinol 

-f-B  naphthol 

-j-  />-toluidin 

-fB  naphthol 

-j-  anil  in 

--  phenol 

--  phenol 

--  aniline 

--  phenylaminobenzo 

thiazole 
-f-  ammonia 
-|-  B  naphthol 
-j-  B  naphthol 
-|-p  cresol 


Color 
Yellow 

Salmon  orange 
Yellow 
Pink 
Brown 
Orange 
Yellow-brown 
Orange-pink 
Yellow-brown 
Orange-pink 

Yellow 
Orange    red 
Brown 

Orange 
Orange   red 

Yellow-brown 
Yellow 
Purple 
Orange 
Brown 


Depth 

Good 

Fair 

Good 

Fair 

Good 


Poor 
Good 


Poor 
Good 


These  colors  are  all  as  fast  to  light,  soap,  bleaching,  etc.,  as 
the  corresponding  azo  colors  from  dehydrothiotoluidin,  and  the 
tinctorial  value  in  general  appears  to  be  much  better,  particularly 
of  the  browns,  where  it  is  really  quite  remarkable.  To  put  it 
colloquially,  "a  little  will  go  a  long  way."  The  specimens 
were  all  dyed  from  a  \%  solution  of  the  amine  in  the 
presence  of  sodium  chloride  according  to  the  method  given  later, 
dried,  and  steam  pressed. 

The  bis-diazo  compounds  are  better  than  the  primary  diazo 
ones,  both  from  a  consideration  of  variety,  and  of  depth  of 
color,  particularly  those  of  alpha  and  beta-napthylamines  from 
which,  as  well  as  those  given,  a  good  series  of  browns  may  be 
obtained.  It  would  be  interesting  and  illuminating  to  determine 
if  a  series  of  greens  could  be  obtained  from  this  base  by  diazo- 
tizing  and  coupling  with  dioxynapthalene  disulphonic  acids,  as 
in  the  case  of  dehydrothiotoluidin,67  but  unfortunately,  the  last 
two  reagents  were  not  available,  and  all  other  attempts  to  pre- 
pare a  green  or  blue  failed,  with  the  exception  of  the  one  purple 
found  in  the  chart,  which,  however,  it  is  interesting  to  note,  be- 
gins to  approach  these  in  structure. 

18.  Para  (2  Bensothiazolyl)  Bcnsoic  Acid 

Paratolyl  benzothiazole  contains  a  methyl  group  which  it  should 
be  possible  to  oxidize  to  the  corresponding  carboxyl  group  by 
methods  analogous  to  other  side  chain  oxidations.  This  was  first 
attempted  by  means  of  potassium  permanganate  in  neutral  solu- 
tion in  the  presence  of  magnesium  sulphate  according  to  Fisher.51 
The  permanganate  was  reduced,  but  the  final  yield  of  the  ex- 

30 


pected  acid  from  5  g.  of  the  thiazole  was  so  small  that  it  could 
only  be  crystallized  once  and  the  amount  was  too  small  to  pro- 
ceed further  with.  The  substance  obtained  was  yellow  white  in 
color  and  appeared  to  decompose,  but  did  not  melt  up  to  270°. 
A  second  experiment  was  performed  using  permanganate  in 
alkaline  solution,  according  to  the  method  of  Bigelow,68  and 
while  the  yield  was  larger  than  in  the  first  case,  .5  g.  from  5  g. 
sample,  it  could  not  be  purified  sufficiently,  for  analysis.  The 
substance  resembled  that  in  the  first  experiment  in  every  way, 
crystallizing  in  microscopic  white  needles  from  alcohol,  which 
darkened  but  did  not  melt  up  to  270°  C. 

19.  Prinmlineazo-Benzoylene   Urea 

It  has  been  shown69  that  1  :3  dioxyquinolin  is  particularly 
suited,  in  combination  with  primuline  diazotized  on  the  fibre 
according  to  the  process  invented  by  A.  H.  Green,  to  give  acid, 
light,  and  wash  fast  orange  colors  on  cotton.  The  procedure  is 
given  in  the  patent,  for  example:  one  requires  for  a  2%  primulin 
developed  color,  a  mixture  of  1%  1 :3  dioxyquinolin  as  the  sodium 
salt,  and  1.5%  sodium  carbonate  in  which  the  material  is  im- 
meresd  after  coming  from  the  diazotizing  bath.  Dioxyquinolin 
gives  a  clear  orange  color  of  greater  acid-,  base-,  and  wash- 
fastness  than  the  corresponding  phenol  or  resorcin  developed 
colors.  It  was  therefore  thought  that  benzoylene  urea  which 
resembles  dioxyquinolin  closely,  would  also  couple  to  give  a  dye 
exhibiting  these  valuable  properties. 

The  procedure  used  in  dyeing  was  a  modification  of  that  de- 
scribed in  the  Badische  Co.  Pocket  Guide,  (p.  101),  and  as  prac- 
tical methods  of  this  kind  are  not  as  readily  accessible  as  might 
be  thought  at  first,  a  brief  summary  is  given. 

(a)  Before  dyeing,  boil  the  cotton  in  a  water  solution  of  so- 
dium carbonate  and  wash  with  water. 

(b)  Enter  the  cotton  into  the  dye  bath    (2%   primulin)    and 
work  at  a  boil  for  1^  hours  adding  5-30  Ibs  of  crystalline  Glau- 
ber's salt  or  2y2  to   10  Ibs.  of  sodium  chloride   for   100  Ibs.  of 
cotton. 

(c)  Dye  cotton  as  just  given  and  treat  for  one-half  hour  in  a 
fresh,  cold  diazotizing  bath,  using  3  Ibs.  of   sodium  nitrite  and 
Sy2  Ibs.  of  concentrated  hydrochloric  acid  per  100  Ibs.  of  cotton, 
keeping  the  temperature  below   50°   F.   by  the   addition  of   ice. 
Add  the  sodium  nitrite  to  the  acid,  not  vice  versa.     (This  is  an 
unnecessary  precaution  for  laboratory  procedure.)     Rinse  once  in 
cold  acidified  water  and  enter  into  the  developer  for  one  hour. 

(d)  A  typical  developer  bath  (for  ingrain  red)   consists  of  a 
\%  solution  of  beta  napthol  dissolved  in  warm  water  by  means 
of  an  equal  weight  of  sodium  hydroxide. 

For  small  amounts  of  material  a  100  c.c.  working  modifica- 
tion of  this  gives  very  good  results.  The  diazotizing  bath  con- 
sists of  17  c.c.  of  concentrated  hydrochloric  acid,  6  g.  of  sodium 

31 


nitrite,  and  200  c.c.  of  water.  The  primulin  in  this  experiment 
was  a  museum  specimen  furnished  by  the  Casella  Co.,  the  ben- 
zoylene  urea  was  a  portion  of  that  prepared  by  Scatchard,70  and 
for  purposes  of  comparison  ingrain  red  (primulin-azo-beta-nap- 
thol)  was  used.  Benzoylene  urea  as  a  developer  gave  a  yellow 
brown  color  that  comes  out  much  more  slowly  than  the  red. 
Tests  for  fastness  were  made  with  these  results: 

Test  B.U.  Yellow  Ingrain  Red 

Boiling  with  5%  HC1  Fast  Fast 

Boiling  with  10%    NaOH  Darkens    slightly  Bleeds  out 

Bleaching  powder  Not  bleached  Not  bleached 

Direct  sunlight — two  weeks  Fades  slightly  more 

than  red 

Soap  solution,  boiling  Fast  Fast 

The  tinctorial  value  of  the  new  dye  is  just  as  good  as  ingrain 
red,  and  it  appears  to  be  of  about  the  same  order  of  fastness  as 
the  latter,  except  to  prolonged  exposure  to  light,  but  this  is  more 
than  counterbalanced  by  its  greater  fastness  to  alkali. 
PART  B — DEHYDROTHIOTOLUIDIN 

This  compound  is  prepared  commercially,  directly  from  para- 
toluidin  and  sulphur,  and  the  methods  are  at  variance  on  two 
principal  points,  the  manner  of  conducting  the  fusion  which  is 
either  by  a  mixture  of  only  the  two  substances  in  molecular  quan- 
tities, or  by  the  addition  of  a  diluent  such  as  napthalene  or  an 
excess  of  partoluidin,  and  the  method  of  purification.  In  any 
event,  much  primulin  and  other  substances  are  formed  simultane- 
ously, and  theitf  formation  is  greater  in  the  presence  of  an  excess 
of  sulphur,  and  since  dehydrothiotoluidin  is  the  more  valuable 
of  the  two,  this  is  to  be  avoided.  Of  the  patents  already  men- 
tioned4* the  basic  ones  are  those  of  Kalle  and  Co.,  of  Biebrich 
am  Rhein  (a  duplicate  of  the  original  one  mentioned  earlier  with 
some  changes),  and  of  Leopold  Casella  and  Co.  Three  methods 
of  separation  of  the  mixed  bases  which  form  the  melt  are  avail- 
able. The  Casella  patent  appears  to  do  so  by  a  difference  in  the 
basicity  of  the  two  compounds,  claiming  that  dehydrothiotoluidin 
is  more  soluble  in  a  30%  by  weight  solution  of  sulphuric  acid, 
while  the  Kalle  patent  effects  this  result  by  taking  advantage  of 
the  fact  that  the  ammonium  salt  of  dehydrothiooluidin  sulphonic 
acid  is  less  soluble  in  water  than  the  corresponding  derivative 
of  primulin.  The  third  method  consists  in  distilling  the  melt  in 
vacuo  by  which  only  dehydrothiotoluidin  comes  over,  but  from  a 
commercial  standpoint  this  method  is  unsatisfactory,  and  although 
it  is  being  used  at  present,  if  there  was  a  way  of  avoiding  it,  it 
would  be  abandoned  due  to  the  difficulties  of  the  process  in  the 
plant. 

Preliminary  experiments  showed  that,  in  spite  of  the  number 
of  patents  and  the  volume  of  literature  on  this  subject,  practical 
directions  for  the  synthesis  were  noticeably  lacking,  and  a  criti- 
cal study  of  all  the  methods  was  made  with  a  view  to  supplying 
this  deficiency  from  a  laboratory  standpoint,  at  least. 

32 


1.   The  Casella  Method 

The  melt  was  prepared  according  to  the  patent  directions  in 
each  case,  substituting  grams  for  "parts"  in  the  wording  of  the 
patent.  After  heating,  the  fusion  mixture  was  repeatedly  ex- 
tracted with  500  c.c.  portions  of  30%,  by  weight,  sulphuric  acid 
until  nothing  further  was  dissolved.  The  liquid  extract  was  then 
drowned  in  water,  or  later  diluted  only  a  little  more,  and  neu- 
tralized while  warm  with  sodium  hydroxide,  which  precipitates 
the  mixed  bases  in  a  form  which  is  more  readily  filtrable.  The 
first  factor  investigated  was  the  effect  of  length  of  heating  time 
on  the  weight  of  the  sulphuric  acid  extract,  and  it  was  found 
that  there  was  very  little  advantage  in  keeping  the  melt  in  fusion 
longer  than  four  hours.  In  extracting  the  melt  it  is  desirable 
to  keep  the  temperature  below  100°  C.  on  a  water  bath,  when 
two  extractions  will  remove  all  of  the  soluble  material  with  a 
minimum  of  impurities.  The  yield  at  this  point,  however,  after 
a  number  of  experiments,  was  never  better  than  33%  of  the  theo- 
retical amount  of  the  substance  from  the  equation : 

2C7H7NH2  +  4S  =  C14H12N2S  +  3H?S 

assuming  the  extract,  for  purposes  of  calculation  only,  to  be  pure 
dehydrothiotoluidin. 

It  was  then  attempted  to  purify  the  product  by  recrystallization 
from  solvents.  The  melting  point  of  the  crude  extract  varies 
from  165°-175°  C.  (uncor.).  A  single  crystallization  of  this  from 
alcohol  will  bring  the  melting  point  up  to  185°,  and  if  this  is 
then  dissolved  in  the  least  amount  of  hot  acetone,  refluxed  with 
boneblack  for  one-half  hour,  filtered,  and  allowed  to  crystallize, 
a  pale  yellow  product  in  small  needle  crystals  melting  at  192°  C. 
(cor.)  is  obtained. 

There  are  two  difficulties  in  this  method.  In  the  first  place 
the  losses  by  the  two  crystallizations  are  so  great  that  it  is  not  a 
satisfactory  method  of  preparation  even  from  a  laboratory  stand- 
point. The  first  one  from  ethyl  alcohol  must  be  done  rapidly 
from  the  hot  solution  as  it  colors  up  and  becomes  tarry  and 
lesinous  quickly,  and  purification  by  crystallization  is  then  impos- 
sible, so  that  of  all  of  the  extract  can  not  be  utilized.  In  the  second 
place  the  composition  of  the  sulphuric  acid  extract  seems  to  be 
decidedly  variable  depending  on  the  physical  conditions  during 
the  extraction,  so  that  there  is  frequently  some  difficulty  in  get- 
ting the  first  solution  to  crystallize  at  all.  as  dehydrothiotoluidin 
does  not  do  so  in  the  presence  of  large  amounts  of  the  higher 
primulines.  It  was  first  thought  that  this  difficulty  was  due  to 
the  presence  and  oxidation  of  paratoluidin  which  can  be  shown 
to  be  present  in  considerable  quantities  even  after  eight  hours 
heating.  (If  the  sulphuric  acid  extract,  instead  of  being  neu- 
tralized with  sodium  hydroxide  as  in  the  later  experiments,  is 
diluted  with  ten  times  its  volume  of  water,  the  bases  are  com- 

33 


pletely  precipitated  and  the  filtrate  will  deposit  nothing  on  further 
dilution,  but  if  it  is  then  neutralized  with  sodium  hydroxide,  a 
copious,  flocculent,  white  precipitate  is  formed  which  can  readily 
be  shown  to  be  paratoluidin.)  The  idea  then  presented  itself  of 
freeing  the  mixed  bases  obtained  from  the  sulphuric  acid  from 
paratoluidin  by  steam  distillation  before  attempting  to  purify  the 
dehydrothiotoluidin  by  crystallization,  but  it  was  found  that  this 
did  not  solve  the  problem  as  the  paratoluidin  apparently  was  not 
responsible  for  the  difficulty.  It  was  subsequently  found  in  the 
literature  that  the  same  suggestion  was  made  by  Jacobson71  in 
one  of  the  earlier  articles,  and  upon  experiment  he  reached  the 
same  conclusion.  It  was  also  found  by  experiment  later  that 
pure  dehydrothiotoluidin  can  readily  be  separated  from  moderate 
amounts  of  paratoluidin  by  crystallization. 

If  the  second  crystallization  is  made  from  cold  acetone  and  the 
boneblack  omitted,  the  substance  crystallizing  out  is  dark  brown 
and  gummy,  does  not  melt  up  to  220°,  and  can  not  thereafter 
be  obtained  as  light  in  color  as  the  preceding  product,  exhibit- 
ing, even  after  a  prolonged  boneblacking  an  orange-yellow  color 
and  slightly  lower  melting  point. 

2.   The  Kalle  Method 

It  was  observed  that  the  relative  amount  of  napthalene  as  re- 
quired in  the  Casella  Method  could  be  varied  greatly,  without 
affecting  the  yield.  (In  order  to  determine  whether  there  was 
compound  formation  between  the  napthalene  and  the  other  sub- 
stances in  the  melt,  a  cooling  curve  was  taken,  which  indicated 
that  there  was  not,  as  may  be  seen  from  the  diagram.)  The 
napthalene  was  then  omitted  entirely,  the  fusion  being  carried 
out  as  directed  in  the  Kalle  patent,  but  extraction  was  still  used 
for  purification,  and  the  yields  and  results  were  the  same  as  those 
just  described.  It  was  therefore  concluded  that  the  claim  that 
the  use  of  napthalene  increases  the  yield  is  unfounded,  its  only 
advantage  being  as  a  temperature  regulator. 

The  method  of  purification  by  vacuum  distillation  was  next 
tried  in  a  preliminary  way.  For  this  purpose  melts  prepared 
by  the  Kalle  method  as  well  as  samples  of  the  crude  material 
made  similarly  by  the  DuPont  Co.,  were  used.  These  melts  dis- 
tilled around  345°  C.  at  a  pressure  of  35  m.m.  and  yielded  a 
product  which  on  a  single  crystallization  from  alcohol  appeared 
in  very  pale  yellow,  odorless  needles  which  on  further  recrystal- 
lization  from  ethyl  alcohol  were  finally  obtained  at  a  constant 
melting  point  of  194.8°  C.  (cor.).  This  was  undoubtedly  pure 
and  probably  the  purest  sample  of  the  compound  which  has  been 
prepared  up  to  this  time.  The  procedure  is  a  difficult  one  to 
carry  out,  the  yields  here  were  less  than  20%  of  the  weight  of 
the  starting  material,  and  the  distillation  was  accompanied  by 
much  foaming  and  decomposition,  the  greater  part  of  the  start- 
ing material  remaining  in  the  flask  as  coke  at  the  end.  As  this 

34 


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was,  however,  finally  concluded  to  be  the  only  feasible  method 
of  purification,  the  complete  details  will  be  given  later. 

3.  Attempt  to  Develop  a  New  Synthesis  of  Dehydrothiotoluidin 
The  work  done  on  the  compound  up  to  this  point  led  to  the  con- 
clusion that  in  order  to  prepare  a  quantity  of  the  substance  suffi- 
cient for  further  investigation,  and  in  a  satisfactory  state  of 
purity,  a  new  synthesis  would  be  highly  desirable.  The  criteria 
for  this  reaction  as  a  laboratory  problem  are : 

(a)  Simplicity  of  mechanical  operations. 

(b)  Large  yield. 

(c)  Avoidance  of   the   formation  of   primulin  which  prevents 
the  satisfactory  crystallization  of  the  compound  without  introduc- 
ing large  quantities  of  other  by-products. 

(d)  Availability  of  starting  materials.     From  consideration  of 
the  general  methods  by  which  thiazoles  have  been  prepared,  the 
following  proposed  syntheses  are  obvious  at  once : 

(a)  Condensation    of    para-amino-meta-thiocresol    with    para- 

amino-benzoyl  chloride. 

(b)  Fusion  of  para-amino-benz-para-toluidid  with  sulphur. 

(c)  Oxidation  of  thio-para-amino-benz-para-toluidid  with  po- 

tassium ferricyanide. 

(d)  Fusion  of  paranitro-benzal-paratoluidin  with  sulphur  anal- 

agously  to  the  patent  method  for  preparing  "Rosenkor- 
per."73  It  was  hoped  that  in  this  reaction,  if  it  occurred 
at  all,  the  hydrogen  sulphide  formed  would  reduce  the 
nitro  group  to  the  amine,  otherwise  a  final  reduction 
would  be  necessary.  This  method  was  chosen  as  the  eas- 
iest to  perform  because  it  is  readily  seen  that  the  required 
SchirFs  base  should  be  easily  obtained  by  condensation 
of  paratoluidin  and  paranitrobenzaldehyde.  This  expec- 
tation was  justified  and  the  compound  was  prepared  just 
before  the  publication  of  the  article  by  Lowy  and  King74 
ori  the  condensation  products  of  paranitrobenzaldehyde  in 
in  which  it  is  described. 

4.  Para  Nitro  Benzal  Paratoluidin 

Large  quantities  of  chromyl  chloride  were  prepared  by  the 
method  of  Law  and  Perkin,75  and  paranitrobenzaldehyde  by  that 
of  V.  V.  Richter.76  . 

Molecular  quantities  of  the  two  substances,  paratoluidin  and 
paranitrobenzaldehyde,  are  dissolved  •  separately  in  the  least 
amounts  of  95%  ethyl  alcohol  and  refiuxed  for  one  hour  after 
mixing.  The  solution  is  evaporated  to  a  small  volume,  allowed 
to  crystallize,  and  the  product  filtered  off  and  recrystallized  from 
ethyi  alcohol.  Paranitrobenzal-paratoluidin  appears  in  pale  yel- 
low needles  melting  at  123°  C.  (cor.).  The  yield  is  only  about 
50%  of  the  theoretical  in  a  pure  state  as  it  is  very  soluble  in 
alcohol  and  the  losses  during  crystallization  are  large. 

36 


5.  Fusion  of  Paranitro-Benzal-Paratoluididc  with  Sulphur 
It   was  expected  that   on   fusion  with   sulphur  this  compound 
would  behave  in  one  of  two  ways,  or  perhaps,  both,  as  follows  : 


resulting  either  in  the  formation  of  dehydrothiotoluidin  or  the 
corresponding  nitro  derivative. 

Accordingly  16  g.  of  the  SchifT  base  and  4  g.  of  powdered 
roll  sulphur  were  mixed  intimately  and  fused  on  an  oil  bath  in  a 
flask  equipped  with  a  reflux  condenser  for  \l/2  hours  at  200°  C. 
Vigorous  '  ebullition  occurred  almost  at  once  and  sulphur  dioxide 
was  evolved  rapidly.  The  mass  became  viscous  at  the  end  of 
three-quarters  of  an  hour  and  was  almost  entirely  solid,  at  tbft 
end  of  one  hour.  Allowed  to  cool,  broke  the  flask  and  pulver- 
ized the  melt,  which  was  black  in  color  and  weighed  16  g.  It 
was  then  extracted  twice  with  concentrated  hydrochloric  acid  in 
100  c.c.  portions  which  were  diluted  with  water,  neutralized  with 
sodium  hydroxide  and  filtered.  The  acid  solution  changed  from 
yellow  to  a  milky  purple  at  the  neutral  point.  A  small  amount 
of  purplish-brown  material,  the  dry  weight  of  which  was  less 
than  1  g.  was  obtained.  The  mass  appeared  to  have  charred  to  a 
large  extent  and  the  yield  was  too  small  to  proceed  further  with. 
It  w'as  not  dehydrothiotoluidin  or  the  nitro  compound,  and  resem- 
bled the  product  obtained  later  from  nitrotoluene  in  every  way. 

It  was  thought  that  a  lower  temperature  might  improve  the 
results,  so  the  experiment  was  repeated  using  xylenes  as  a  diluent 
and  temperature  regulator. 

A  mixture  of  12  g.  of  paranitro-benzal-paratoluidin,  55  c.c. 
of  xylenes,  and  3  g.  of  sulphur,  was  refluxed  for  5  hours,  the 
mixture  was  then  diluted  with  water  and  steam  distilled,  and  the 
xylene  recovered  from  the  distillate.  The  residue  in  the  flask 
consisted  of  a  dark  brown  solid  and  a  yellow  substance,  more 
of  which  is  deposited  in  yellow1  needles  from  the  water  solution 
on  cooling.  Filtered  and  separated  the  yellow  needles  from  the 
brown  material  which  was  present  in  large  lumps.  None  of  the 
starting  material  was  obtained  from  this,  although  the  brown  mass 
did  contain  free  sulphur.  The  products  of  the  reaction  were  the 
brown,  amorphour,  insoluble  material,  and  the  yellow  crystals, 
which  are  soluble  in  alcohol  from  which  they  crystallize  in  small 
crystals'  of  indistinguishable  shape,  melting  at  227-228°  C  (cor.). 
The  water  solution  of  this  compound  is  acid  to  litmus,  qualitative 
analysis  showed  the  presence  of  carbon,  hydrogen,  and  nitrogen, 
and  a  sample  gave  the  reduction  test  for  the  nitro  group.  It 
was  not  investigated  further  as  it  was  evidently  not  the  desired 
sulphur  base. 

37 


6.  Fusion  of  Paranitrotoluene  and  Sulphur 
At  this  point  the  thought  suggested  itself  that  paranitrotoluene 
should  yield  dehydrothiotoluidin  or  its  nitro-body  on  fusion  with 
sulphur  by  reactions  similar  to  those  already  given. 

(a)  2CHS.C6H4N(X  +  2S  =  C14H12N,S  +  SOX  +  2H,O 

(b)  2CH3.C6H4N02  +    S  =  C14H10N2"S02  +  2H2O 

A  mixture  of  30  g.  of  paranitrotoluene  and  15  g.  of  sulphur 
was  heated  under  a  reflux  condenser  and  for  two  hours  sulphur 
dioxide  was  evolved  vigorously.  The  melt  which  on  cooling 
weighed  29  g.,  was  powdered  and  extracted  three  times  with 
100  c.c.  portion  of  concentrated  hydrochloric  acid  which  were  then 
drowned  in  ten  times  their  volume  of  water.  On  standing  a  dark 
brown  flocculent  precipitate  settled  out,  and  was  filtered  off  and 
dried.  It  blackened  up  somewhat  on  standing,  and  weighed  7  g. 
when  dry.  The  extract  was  pulverized  and  warmed  with  100  c.c. 
of  ethyl  alcohol,  filtered  and  the  deep  red  solution  was  evaporated 
down  and  allowed  to  crystallize,  yielding  about  a  gram  of  light 
brown  micro-crystals  that  appeared  to  sublime  or  decompose 
around  230°  C.  Qualitative  analysis  showed  the  presence  of 
carbon,  hydrogen,  nitrogen,  and  sulphur.  Zinc  dust  in  50%  ethyl 
alcohol  appears  to  react  with  the  substance  as  it  gives  a  yellow 
solution  with  a  pale  green  fluorescence,  but  the 'reaction  mixture 
does  not  reduce  ammoniacal  silver  nitrate  and  consequently  the 
original  substance  is  not  a  nitro'  compound. 

Gatterman  and  Neuberg77  prepared  dehydrothiotoluidin  from 
thio-paranitro-benztoluid  by  the  Jacobson  reaction.  They  describe 
the  nitro  compound  as  crystallizing  in  yellow-red  needles  from 
glacial  acetic  acid,  and  none  of  the  above  mentioned  substances 
resembles,  even  slightly,  this  or  dehydrothiotoluidin. 

The  substance  obtained  in  this  reaction  is  a  sulphur  compound, 
probably  identical  with  that  obtained  from  para-nitro-benzal-para- 
toluidid,  has  some  tinctorial  value,  and  does  not  correspond  to 
any  that  have  been  prepared.  As  it  can  be  made  easily  in  moder- 
ately large  quantities,  it  might  be  worth  while  to  investigate  the 
reactions  further,  but,  as,  for  the  preparation  of  dehydrothioto- 
luidin, these  experiments  failed,  this  was  not  done. 

7.  Apparatus  for  the  Vacuum  Distillation  of  Dehydrothiotoluidin 
After  attempting  to  prepare  the  compound  in  fairly  large  quan- 
tities by  all  of  the  known  methods,  and  unsuccessfully  trying  to 
develop  a  new  one,  it  was  finally  concluded  that  the  Kalle  method 
offered  the  only  possibility,  and  purification  must  be  accomplished 
by  vacuum  distillation.  Preliminary  work  showed  that  the  diffi- 
culties were  mainly  iow  yields  and  the  tendency  of  the  compound 
to  swell  up  and  run  over  during  the  process  of  distillation  mak- 
ing it  impossible  at  first  to  obtain  more  than  10  g.  of  the  com- 
pound by  this  method  in  a  single  operation  on  a  laboratory  scale. 
The  apparatus  first  tried  was  the  ordinary  vacuum  distillation 
set  up.  At  the  lowest  pressures  obtainable  with  a  good  water 

38 


Vacuum  Distillation  Appai  aitis 


to  pump 


to  pump 


pump 


pump  (20-30  m.m.),  dehydrothiotoluidin  distills  around  350°  C, 
and  it  was  found  impossible  to  maintain  a  good  vacuum  at  this 
temperature,  using  cork  stoppers  with  the  additional  difficulty  of 
more  rapid  decomposition  as  the  pressure  rose,  while  further,  the 
narrow  tube  clogs  up  almost  at  once.  The  first  step  was  to  modify 
the  apparatus  as  shown  in  the  diagram  (Fig.  1),  the  flasks  being 
250  c.c.  Pyrex  ones  sealed  together,  and  then  the  whole  apparatus 
was  sealed  up  after  the  insertion  of  the  mixed  bases.  The  heat- 
ing w'as  done  over  a  free  flame.  This  had  the  disadvantage  of 
ordinarily  only  being  capable  of  one  run  of  50  g.  of  mixture 
(if  more  is  used  it  will  run  over,  because  of  the  foaming  and 
decomposition),  as  it  requires  too  great  a  degree  of  manipulative 
skill  to  cut  off  the  different  parts  at  the  end  of  the  operation  and 
then  to  seal  them  together  again,  it  being  less  trouble  to  make  a 
new  apparatus,  and  in  addition  the  closed  arrangement  did  not 
give  sufficient  control  of  the  run. 

The  next  improvement  (Fig.  2)  was  to  draw  out  the  neck  of 
the  distillation  flask,  pack  the  upper  part  with  asbestos,  and  then 
close  with  a  rubber  stopper,  through  which  a  thermometer  can 
be  inserted,  which  is  protected  from  the  heat  by  the  asbestos. 
This  was  a  decided  advance,  as  two  or  three  successive  small 
amounts  (50  g.)  of  mixed  bases  can  be  placed  in  the  main  flask 
and  distilled  before  it  is  necessary  to  break  the  apparatus  to 
remove  the  yield,  which  disadvantage  still  remains. 

The  final  and  best  type  of  apparatus  is  shown  in  Fig.  3.  The 
distillation  flask  is  a  500  c.c.  Pyrex  one  connected  to  a  250  c.c. 
receiver  by  a  6-inch  length  of  Pyrex  tubing  of  the  same  bore  as 
the  neck  of  the  smaller  flask.  The  set-up  is  evacuated  through 
the  neck  of  the  receiver  and  it  is  strongly  recommended  to  place 
a  U-tube  of  cotton  wool  between  the  safety  bottle  and  the  water 
pump  during  distillation,  as  otherwise,  in  spite  of  the  best  of 
cooling,  the  vapors  will  be  carried  along  and  clog  up  the  water 
pump  during  distillation,  and  while  this  is  being  remedied  there 
will  be  much  loss  of  yield  due  to  charring.  Cooling  is  accom- 
plished by  immersing  the  receiver  in  a  water-bath. 

In  this  apparatus  100  g.  (not  more!)  of  the  mixed  base  can 
be  distilled  at  one  run,  yielding  after  crystallization  of  the  dis- 
tillate once  from  96%  alcohol  22-25  g.  of  pure  dehydrothioto- 
luidin. To  avoid  overheating,  the  distillation  flask  was  heated 
in  a  sodium  nitrate  bath  but  this  was  discarded  as  it  was  too 
difficult  to  control  the  foaming  which  inevitably  accompanies  the 
operation.  If  the  distillation  is  done  rapidly  with  a  large  free 
flame  which,  also  heats  the  delivery  tube,  this  can.  be  readily  done 
by  removing  the  flame  and  increasing  the  pressure  judiciously 
from  the  stop-cock  of  the  safety  bottle  when  the  melt  appears 
to  be  about  to  run  over,  and  when  it  has  subsided  distillation 
can  be  continued. 

The  advantages  of  this  apparatus  are  as  follows: 

40 


(1)  The  pure   dehydrothiotoluidin   can  be  easily  removed  by 
running  hot  alcohol  through  the  delivery  tube  into  the  receiver 
by  means  of  a  rubber  tube  inserted  into  the  neck  of  the  distilla- 
tion flask,   which  loosens   it   up,   and  it  can  then  be  broken  up 
by  shaking,  and  careful  manipulation  of  a  glass  rod,  and  taken 
out. 

(2)  The  apparatus  can  then  be  readily  cleaned  by  soaking  in 
hot  concentrated  sulphuric  acid  and  so  can  be  used  repeatedly. 

(3)  The  product  obtained  is  pure  and  in  good  quantity,  and 
the  decomposition  which  accompanies  the  distillation  can  be  con- 
trolled as  all  parts  of  the  apparatus  are  accessible  at  all  times. 

8.  Preparation  of  Pure  Dehydrothiotoluidin 
As  a  result  of  the  work  described,  the  following  procedure 
for  the  preparation  of  the  pure  compound  was  arrived  at.  This 
method  unlike  any  of  the  previous  ones  found  in  the  literature, 
is  complete  as  far  as  laboratory  directions  are  concerned,  will 
work  exactly  as  recorded,  and  was  used  for  the  preparation  of 
considerable  quantities  of  the  pure  base. 

110  g.  of  paratoluidin  and  60  g.  of  powdered  roll  sulphur  are 
heated  from  4  to  6  hours  in  a  one  liter  flask  equipped  with  a 
reflux  air  condenser  on  an  oil  bath  at  220°.  At  the  end  of  this 
time  the  melt  is  poured  out  into  an  evaporating  dish  or  a  mold 
made  of  the  lid  of  a  flat  paper  or  wooden  box,  and  powdered 
after  cooling.  It  should  weigh  about  100  g.,  depending  on  how 
much  can  not  be  poured  from  the  flask,  but  not  more  than  this 
is  used  in  the  subsequent  distillation. 

The  distillation  is  then  conducted  in  the  apparatus  in  Fig.  3 
following  the  directions  and  precautions  already  given.  The  prod- 
uct is  recrystallized  once  from  96%  ethyl  alcohol  which  gives 
22-25  g.  of  yellow  needles  melting  at  192-193°  C.  (cor.).  Fur- 
ther recrystallization  and  boneblacking  will  yield  it  still  paler  in 
color  and  melting  at  194.8°  C.  (cor.)  as  already  described. 

9.   Benzal-Dchydrothiotoluidin 

To  a  saturated  solution  of  dehydrothiotoluidin  in  alcohol,  add 
the  calculated  amount  of  benzaldehyde  from  the  equation : 

C14H12N,S  +  C7H60  =  C21H16N2S  +  H2O 

Heat  to  boiling  for  a  few  minutes  and  allow  to  stand  to-  crystalli- 
zation. The  yield  is  practically  quantitative  and  this  method  may 
be  conveniently  used  to  recover  the  base  from  the  solutions  re- 
maining from  its  purification,  as  the  condensation  product  is  much 
less  soluble  in  96%  ethyl  alcohol  than  the  dehydrothiotoluidin 
itself.  Recrystallize  the  product  from  alcohol  in  which  it  gives 
a  pale  yellow  strongly  fluorescent  solution,  and  from  which  it 
appears  in  very  pale  yellow,  odorless,  glistening  plates  melting 
at  193°  C.  (cor.). 

Calculated   for   C^H^NoS  S  =  9.76% 

Found  S  =  9.80% 

41 


10.  Dehydrothiotoluidin  in  the  Atophan  Reaction 
Dehydrothiotoluidin  being  a  primary  amine  should  condense 
with  benzaldehyde  and  pyruvic  acid  to  give  a  methyl  benzothi- 
azolyl  atophan  similarly  to  the  reaction  which  Dobner  and  Gies- 
iecke78  found  that  aniline  underwent.  The  reaction  was  therefore 
tried  following  this  method  but  substituting  the  molecular  quan- 
tity of  the  sulphur  base  for  the  aniline.  The  benzaldehyde  con- 
densation product  was  isolated  from  the  reaction  mixture,  but  no 
new  compound  corresponding  to  atophan  was  found,  although 
small  amounts  of  an  amorphous  brown  material  soluble  in  tolu- 
ene, but  insoluble  in  sodium  carboniate  and  hydroxide,  were 
formed. 

The  experiment  was  repeated  using  the  benzal-dehydrothioto- 
luidin  instead  of  the  two  substances  individually,  but  after  24 
hours'  heating  practically  all  of  the  material  was  recovered  un- 
changed, although  small  amounts  of  an  amorphous,  highly  insolu- 
ble brown  material  were  formed.  Dehydrothiotoluidin  apparently 
will  not  condense  to  form  a  substituted  atophan. 

11.  6(6-Methyl  Benzothiazolyl)    Quinolin 

Like  other  primary  amines,  dehydrothiotoluidin  should  con- 
dense with  glycerine  in  the  presence  of  sulphuric  acid  and  an 
oxidizing  agent  such  as  nitrobenzene/9  arsenic  acid,80  ferric  sul- 
phate,81 etc.,  to  yield  a  quinolin  of  the  structure: 


. 


AA 

X) 


if  the  reaction  proceeds  analagously  in  this  case. 

The  method  of  Skraup79  was  first  used,  it  having  previously 
been  found82  that  practically  no  quinolin  results  from  reaction 
of  the  reduced  nitrobenzene  during  the  reaction.  56  g.  of  crude 
Casella  dehydrothiotoluidin  and  proper  molecular  quantities  of 
the  other  substances,  were  heated  according  to  the  directions. 
The  reaction  mixture  turned  red  at  once,  and  a  reddish,  oily  tar 
formed  on  the  surface  as  the  reaction  proceeded,  a  yellow  solid 
forming  on  the  bottom  toward  the  end  of  the  reaction  when  the 
mass  became  very  viscous  and  boiling  slowed  up.  The  mass 
solidified  on  cooling,  300  c.c.  of  water  were  added  and  it  was 
distilled  with  steam  to  remove  the  nitrobenzene.  The  residue  in 
the  flask  was  neutralized  with  warm  sodium  hydroxide,  filtered 
and  dried,  and  distilled  in  vacuo,  as  it  was  expected  that  the 
new  compound  would  probably  be  a  solid  because  of  its  high 
molecular  weight,  and  complex  structure,  a  conclusion  which  was 
later  justified.  A  small  amount  of  yellow  solid  distilled  over  with 
a  vile  smelling  liquid.  The  solid  was  filtered  off  and  dissolved 
in  concentrated  hydrochloric  acid  from  which  it  was  precipitated 
with  water.  It  was  recrystallized  from  hot  alcohol,  and  the  red, 
fluorescent  solution  deposited  small  light  brown  crystals  (1  g.), 

42 


with  a  tobacco-like  odor,  melting  at  142°  C.  (uncor.) 

The  use  of  the  crude  dehydrothiotoluidin  was  thought,  how- 
ever, to  offer  too  many  other  possibilities,  so  the  reaction  was 
repeated  using  pure  material,  and  following  the  method  of  Kneup- 
pel,  with  appropriate  modifications  for  the  different  physical 
properties  of  the  new  substance,  which  was  expected  to  give  a 
better  yield. 

15  g.  (.07  moles.)  of  pure  dehydrothiotoluidin  is  dissolved 
in  20  c.c.  of  concentrated  sulphuric  acid  which  is  slightly  more 
than  the  amount  necessary  in  the  original  method  but  is  required 
because  of  the  physical  properties  of  the  amine,  and  21.7  g.  of 
glycerine  and  10.6  g.  of  arsenic  acid  were  added  to  the  solution 
in  a  one  liter  flask  equipped  with  an  air  condenser.  The  large 
flask  is  necessary  because  the  reaction  is  vigorous  and  the  mix- 
ture foams  up  and  will  run  all  the  way  up  the  condenser  other- 
wise. The  mixture  is  heated,  is  red  at  first,  but  vigorous  ebulli- 
tion soon  begins  and  continues  even  if  the  flame  is  removed, 
and  turns  brown  as  the  reaction  proceeds,  the  mixture  foaming 
up.  The  temperature  is  kept  constant  at  190°  by  means  of  an 
oil  bath.  Stop  heating  after  \l/2  hours,  cool  and  add  500  c.c. 
of  water.  Continued  shaking  gives  a  deep  brown  solution  that 
appears  homogeneous. 

Neutralize  with  solid  sodium  hydroxide.  The  solution  becomes 
light  brown  at  the  neutral  point  and  deposits  a  black,  tarry  mate- 
rial, which  is  involatile  and  can  not  be  distilled  with  steam. 

Filter  off  and  dry  the  black  solid.  Distill  in  vacuo  in  the 
apparatus  designed  for  dehydrothiotoluidin.  The  mass  melts, 
and  the  product  distills  over  around  250°  C.  at  45  m.m.  pressure. 
A  small  amount  of  water  arid  thiophenols  distills  over  with  it. 
and  the  product  is  therefore  crystallized  from  ethyl  alcohol  in 
which  it  gives  an  orange-red  fluorescent  solution.  Methyl-thiazlyl- 
quinolin  appears  in  miscroscopic  pale  brown  crystals  melting  at 
147°  C.  (cor.).  The  yield  is  2.5  g.  or  15%  from  the  equation: 

C14H12N,S  +  C3H803  =  C17H12N2S  +  4H2O 
The  product  was  identical  with  that  obtained  in  the  first  experi- 
ment, and  has  a  characteristic  faint  tobacco-like  odor. 

Qualitative  analysis  showed  the  presence  of  carbon,  hydrogen, 
nitrogen,  and  sulphur,  and  the  compound  was  analyzed  for 
sulphur. 

Calculated  for  C17H19N2S  S=    11.59% 

**-  .      .  .         HIS 

The  new  base  is  a  typical  quinolin  and  adds  methyl  iodide 
directly,  a  mixture  of  equal  moles  of  this  and  quinaldin  methio- 
dide  reacting  in  the  presence  of  caustic  alkali  to  produce  a  sub- 
stance of  a  deep  purple-red  color,  analagously  to  quinolin  itself. 
The  product  is  probably  of  the  cyanine  type  and  it  would  be 
interesting  to  investigate  the  further  condensation  of  methyl- 

43 


benzothiazolyl  quinolin  methiodide  with  this,  lepidin,  other  sub- 
stituted quinolins,  as  well  as  with  2-methyl-benzothiazole  which 
Hofmann,  as  has  already  been  mentioned,  observed  to  undergo 
similar  reactions. 


DISCUSSION  AND  CONCLUSIONS 

1.  The   thiazole    structure   does   not   appear   to    function   as   a 
chromophore,  or  at  least,  functions  very  poorly.     A  large  number 
of   benzothiazoles   have  been  described   in  this   paper,   and   they 
are   representative   ones,  of   which   as   has   been   seen,   the  large 
majority,   even  of   those   which  contain  groups   which  are   ordi- 
narily accepted  as  auxochromes,  such  as  the  hydroxy,  the  hydro- 
sulphide,  methoxy,  ethoxy,  nitro  (which  is  also  a  chromophore), 
etc.,   are  colorless,   and  the  remainder  in  a   pure  state  are  only 
faintly  colored,  as  dehydrothiotoluidin,  and  are  not  dyes.     The 
primulins  and  chromins  are  exceptions  but  do  not  furnish  a  valid 
objection  to  this  conclusion,  as  their  structure  is  not  yet  estab- 
lished.    In  the  dyes  of  this  series,  it  is  therefore  concluded,  the 
chromophore  must  be  the  azo  or  other  group,  though  the  thiazole 
structure  may,  and  probably  does  play  an  important  part  in  modi- 
fying the  colors  obtained. 

2.  The  thiazole  structure  is  not  an  odorophore.     The  odorifer- 
ous compounds  as  may  be  seen  from  Hofmann's  work  and  other 
investigations  described  herein,  are  closely  related  to  the  mother 
substance,   benzothiazole,   and  the   farther  we  get   from  this  by 
substitution,  the  fainter  the  odor  becomes.     In  the  odorous  com- 
pounds, as  has  been  previously  observed,   the  smell   is  strongly 
suggestive  of  pyridine  and  the  other  nitrogen  bases,  and  appears 
to  be  associated  with  the  tertiary  nitrogen  atom.     This  is  fur- 
ther borne  out  by  another  fact  developed  in  this  paper.     Dehydro- 
thiotoluidin  is   odorless   but   the  benzothiazolyl    quinolin    synthe- 
sized   from   it   has   again   the  typical   plant-base   odor   somewhat 
resembling  nicotine,  which  it  acquires  on  the  introduction  of  the 
second  tertiary  nitrogen  atom.     The  peculiarly  aromatic  odor  of 
"Rosenkorper"    is   hence   a   purely    fortuitous    circumstance    and 
indeed,  the  odor  of  this  when  in  a  pure,  dry  state  is  very  faint, 
and  it  requires  some  stretch  of  the  imagination  to  be  reminded 
of   "tea-roses  and  geraniums." 

3.  The  commercial  methods  by  which  dehydrothiotoluidin  is 
being  prepared  at  present  give  yields  of  the  base  which  do  not 
exceed  35%  and  some  of  this  must  necessarily  be  lost  in  subse- 
quent purification.     From  the  work  done  in  this  paper,  the  direct 
separation  of  dehydrothiotoluidin  and  primuline  if  formed  in  the 
same  mixture  with  other  substances,  does  not  seem  to  be  possible 
(other  than  by  distillation)  if  by  such  a  method  is  meant  one  which 
will  give  large  yields  of  the  base  in  a  state  of  purity  indicated 
by  good  crystalline  form,  and  a  melting  point   of    191°  or  over. 

44 


The  problem  must  be  solved  by  the  discovery  of  a  method  of  syn- 
thesis which  will  avoid  entirely  the  simultaneous  formation  of 
primulin,  if  it  is  to  be  solved  at  all. 

SUMMARY 

1.  A  fairly  complete  resume  of  previous  work  in  the  benzo- 
thiazole  field  has  been  given,  the  chief  contribution  of  the  investi- 
gators noted,  and  some  attractive  lines  for  further  research  have 
been  indicated. 

2.  The  following  new  compounds  have  been  prepared : 

2  Paratolylbenzothiazole 

Nitroparatolylbenzothiazole 

Aminoparatolylbenzothiazole 

22  azo  dyes  from  aminoparatolyl  benzothiazole 

Tri    (2  anilinobenzothiazolyl)   carbinol 

Di  (2  benzothiazolyl)  fuchsone  benzothiazolylimine 

Primulin  azo  benzolyene  urea 

Paranitrobenzal  paratoluidin 

Benzaldehydrothiotoluidin 

6(6  methyl  benzothiazolyl)  quinolin  . 

3.  From  the  consideration  of  about  one  hundred  compounds  of 
the  benzothiazole  group,  including  those  prepared  in  the  course 
of  this  work,  and  others  described  by  previous  workers,  it  has 
been  concluded  that  the  thiazole  structure  is  not  a  chromophore. 

4.  Of  all  the  compounds  given,  only  seven  have  characteristic 
odors,  and  only  one  has  one  which  differs  from  what  we  should 
expect  from  structural  considerations  of  genetic  relationship.     It 
is  therefore  concluded  that  the  thiazole  structure  is  not  an  odor- 
phore. 

5.  Apparatus  has  been  developed  and  a  laboratory  method  has 
been  given  for  the  preparation  of  dehydrothiotoluidin  in  a  state 
of  purity,  which,  judged  by  its  melting  point   (194.8°  C,  cor.), 
has  not  been  attained  by  previous  workers,  and  a  critical  study 
has  been  made  of  the  reactions  and  processes  by  which  it  is  being 
obtained  at  present. 


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46 


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63.  (See  3). 

64.  Hofmann,  Berichte,  20.  1176   (1887). 

65.  (See  36). 

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MISCELLANEOUS    REFERENCES 

For  patents  dealing  with  azo  dyes  from  dehydrothiotoluidin  and 
others  see : 

Friedlander,  "Fort,  der  Thccrfarbcnfabrikation"   (all  volumes). 

Winther,  "Patents  in   Organic   Chemistry." 
For  general  information  regarding  sulphur  dyes : 

Cain  and  Thorpe,  "Dyestuffs  and  Intermediates." 

Knecht,   Rawson,  Lowenthal,  "Manual  of  Dyeing." 

Fay,  "Coal  Tar  Dyes." 

Richter  Lexicon,  Beilstein,  Schulz  and  Julius,  etc. 

47 


BIOGRAPHICAL  NOTE 

Martin  Meyer  was  born  in  St.  Louis,  Missouri,  on  April  15, 
189  .  He  graduated  from  the  College  of  the  City  of  New  York 
in  1918,  receiving  the  degree  of  Bachelor  of  Science  cum  hnulc, 
and  from  there  pursued  graduate  work  in  chemistry  under  the 
Faculty  of  Pure  Science  at  Columbia  University,  at  which  he 
was  awarded  the  degree  of  Master  of  Arts  in  1920. 

At  present  an  instructor  in  chemistry  at  the  College  of  the 
City  of  New  York,  he  is  also  a  member  of  the  American  Chemi- 
cal Society,  and  of  Phi  Beta  Kappa,  Phi  Lambda  Upsilon,  and 
Sigma  Xi,  honorary  scholarship  and  scientific  fraternities,  re- 
spectively. 


CLARK 

NEW    Y< 


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